Britain currently has 17 F-35Bs and has pledged to purchase 138 in total from US aviation giant Lockheed Martin.
The aircraft - which cost almost £100m - can land vertically, similar to the Harrier Jump Jet, and combine radar-evading stealth technology with supersonic speeds.
Six of the jets have been deployed at RAF Akrotiri in Cyprus since May for training exercises, in an operation known as Exercise Lightning Dawn.
As part of their training, the jets carried out 95 missions and flew in pairs for 225 hours, the MoD said.
They have now joined the hunt for militants under Operation Shader, the UK's contribution in the ongoing military action against IS.
Speaking from the Cypriot RAF base, Ms Mordaunt said she was "very proud that these are now flying in defence".
She added: "It obviously has some incredible capabilities which are really putting us in the lead."
The jets, jointly operated by the RAF and the Royal Navy, are expected to take off from the decks of the new £3.1bn Queen Elizabeth Class aircraft carrier in the autumn for more testing.
Why F-35 jets' real test is still to come
By BBC defence correspondent Jonathan Beale
The first of Britain's most advanced and expensive fighter jets have now carried out more than a dozen missions over Iraq and Syria.
With IS having lost its territory and on the run there are now few obvious targets.
The F-35s have not yet conducted any airstrikes. Instead they've been using their sophisticated sensors to gather intelligence.
The RAF describes the F-35 as the best "eyes and ears" on the battlefield, even though the jet is still suffering from a host of technical problems.
But its other great asset is that it is hard to see. Britain's first "stealth" jet can, in theory, avoid detection by enemy radar.
The real test in combat will not be against the remnants of IS, but a well armed opponent with advanced air defences.
Britain currently has 17 F-35Bs and has pledged to purchase 138 in total from US aviation giant Lockheed Martin.
The aircraft - which cost almost £100m - can land vertically, similar to the Harrier Jump Jet, and combine radar-evading stealth technology with supersonic speeds.
Six of the jets have been deployed at RAF Akrotiri in Cyprus since May for training exercises, in an operation known as Exercise Lightning Dawn.
As part of their training, the jets carried out 95 missions and flew in pairs for 225 hours, the MoD said.
They have now joined the hunt for militants under Operation Shader, the UK's contribution in the ongoing military action against IS.
Speaking from the Cypriot RAF base, Ms Mordaunt said she was "very proud that these are now flying in defence".
She added: "It obviously has some incredible capabilities which are really putting us in the lead."
The jets, jointly operated by the RAF and the Royal Navy, are expected to take off from the decks of the new £3.1bn Queen Elizabeth Class aircraft carrier in the autumn for more testing.
Why F-35 jets' real test is still to come
By BBC defence correspondent Jonathan Beale
The first of Britain's most advanced and expensive fighter jets have now carried out more than a dozen missions over Iraq and Syria.
With IS having lost its territory and on the run there are now few obvious targets.
The F-35s have not yet conducted any airstrikes. Instead they've been using their sophisticated sensors to gather intelligence.
The RAF describes the F-35 as the best "eyes and ears" on the battlefield, even though the jet is still suffering from a host of technical problems.
But its other great asset is that it is hard to see. Britain's first "stealth" jet can, in theory, avoid detection by enemy radar.
The real test in combat will not be against the remnants of IS, but a well armed opponent with advanced air defences.
A report on how to avoid checks on the Irish border after Brexit suggests the UK and Ireland could try to form a new single zone for food standards.
The radical proposal is part of the Alternative Arrangements report.
It is backed by Tory MPs Nicky Morgan and Greg Hands.
Food standards are one of the most difficult border issues due to strict EU rules as food products entering from a non-member state must be subject to checks at the point of entry.
If the UK is outside the single market after Brexit that could mean products being exported from Northern Ireland to the Republic would have to be checked at border inspection posts.
The report from the Alternative Arrangements Commission suggests that one solution could be for Britain and Ireland to form a single zone for food standards.
The rules in the zone would remain closely aligned with the EU to minimise the prospect that goods would have to be checked when entering the continental EU.
If the UK sought to diverge from EU rules then Ireland could revert to the EU regulatory area.
In that scenario, Stormont would then have a vote on whether it wanted to remain aligned with Ireland - which would mean new checks on goods coming into NI from the rest of the UK.
The proposal is likely to face some major hurdles and the commission acknowledges it would be difficult to negotiate.
It would require the EU to accept UK standards as equivalent to EU standards.
It is likely to be extremely controversial in Ireland as it could be seen as weakening Ireland's position as a member of the EU single market.
It is also not a guarantee that border checks would not ultimately have to be applied.
The island of Ireland is already a single zone for animal health, meaning all livestock entering NI from GB are subject to checks at Larne Harbour.
The commission says that simply extending that arrangement to cover food standards would resolve many issues.
However, it concludes that such an arrangement could not negotiated at this time, though that could change if a Stormont government is in place.
Another idea around the area of food standards suggests that any checks could take place away from the border.
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That could mean, for example, Irish government accredited vets inspecting food production facilities in Northern Ireland.
The EU rules on Border Inspection Posts currently allow inspection to happen away from the border if the frontier area has "geographic constraints".
The Commission suggests this could also be explored in an Irish context.
The geographic constraints rule can apply if a border crossing is somewhere like a narrow mountain pass which would make it hard to construct inspection posts.
That would not seem to apply on somewhere like the main Belfast - Dublin road.
Last week, the UK government announced the first of three expert groups which will also look at "alternative arrangements".
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Your guide to Brexit jargon
The EU has also committed to exploring alternative arrangements once a Withdrawal Agreement is passed.
On Friday, the Taoiseach (Irish prime minister) emphasised that whatever alternative arrangements may be proposed any Brexit deal must also include the backstop.
Speaking at the end of an EU summit Leo Varadkar said: "We can't accept that alternative arrangements are an alternative to a backstop unless we see what they are, know how they would work and see them demonstrated.
"That hasn't been done yet and I don't see that being done this side of 31 October, which is why we certainly can't accept the deletion of the backstop."
Sources said that the Foreign Office’s minister for the Middle East Dr Andrew Murrison is having “senior-level talks with his counterpart and other officials”.
News of the mission to the Islamic Republic came as it emerged Iran executed a former defence ministry employee accused of spying for the US.
US State Department sources have warned the threat of military confrontation will not subside while Donald Trump pursues his policy of “maximum pressure” of economic sanctions, aimed at striking a comprehensive deal with the regime.
Last month Congress was told that pressure is having an effect in Iran, with funding to sections of the military being slashed.
This, they say, leaves Tehran waiting to see whether the US president secures a second Oval Office term next year.
Last week, both countries seemed to have their “Cuban missile crisis” moment after the downing of a US Global Hawk surveillance drone over international waters near Iran.
Mr Trump confirmed he came within “10 minutes” of authorising a strike on Iranian facilities but called it off after learning there would be 150 casualties.
He later clarified that the carrier-borne aircraft were within two hours of launching.
Last night Tehran said it had executed ex-aerospace technician Jalal Hajizavar for spying.
It follows recent claims that the Islamic Republic disrupted a “major CIA ring” of sympathetic cyber spies operating from within Iran and other countries.
Next month, President Hassan Rouhani’s Iran is expected to exceed the enriched low-grade uranium it is allowed under the terms of the JCPOA, the Iran nuclear deal, from which Mr Trump withdrew after assuming office.
Britain still ostensibly backs the deal, along with China, France, Germany and Russia, but privately, diplomats say the US pull-out has left it defunct.
On Friday, Mr Trump blamed the current situation with Iran on decisions by his predecessor, Barack Obama, to ratify that deal, claiming it “gave them $150billion, and $1.8billion in actual cash, and a free path to nuclear weapons”.
He tweeted that following the drone attack, he had been “cocked and loaded” and within 10 minutes of launching strikes on three targets within Iran. He wrote: “When I asked how many will die. 150 people, sir, was the answer from a General. 10 minutes before the strike I stopped it, not proportionate to shooting down an unmanned drone.
“I am in no hurry, our Military is rebuilt, new, and ready to go, by far the best in the world. Iran can NEVER have Nuclear Weapons, not against the USA, and not against the WORLD!”
Shortly after posting the tweets, Mr Trump seemed relaxed and was pictured holding a baby at the Congressional Solstice picnic at the White House.
Congressional leaders who attended a secret briefing on the potential strikes the day before said he seemed genuinely reluctant to push the button.
“We know Trump wants to avoid conflict at all costs. Even before his tweet, there was a controlled message from the administration explaining he had stood down,” said regional analyst Kyle Orton.
“Everything we know about him suggests that he would not have made that strike. It’s an attempt to get leverage and force Tehran to the table for what he calls a better deal.”
But others said the tension between the countries will remain for the foreseeable future.
Richard Nephew, the Obama government’s sanctions expert, said: “There is a view that now both countries have had a good scare, they may broker new diplomatic relations through Oman.
“But what’s more likely is we give it a couple of weeks, until Iran resumes its uranium enrichment programme, before we see a re-escalation of rhetoric.”
Mr Nephew said all Democratic election frontrunners were pledging to re-engage the US with the JCPOA, adding: “It’s safe to say Tehran is waiting for 2020 and whether Trump wins again.”
Meanwhile, London mayor Sadiq Khan kept up his war of words with Mr Trump yesterday, labelling the US leader “a 6ft 3 child in the White House”.
Mr Trump has previously called Mr Khan a “stone cold loser” and mocked his height.
LONDON (Reuters) - Reports of a heated late-night row between Boris Johnson and his girlfriend sparked a debate on Sunday about whether it would hurt his campaign to be Britain’s next prime minister and the front-runner’s suitability for the job.
Boris Johnson, a leadership candidate for Britain's Conservative Party, gestures during a hustings event in Birmingham, Britain, June 22, 2019. REUTERS/Hannah McKay
Polls conducted for the Mail on Sunday newspaper before and after front page reports of the argument showed that Johnson’s lead over rival Jeremy Hunt, the foreign minister, had evaporated amongst all voters and had narrowed among Conservatives.
Johnson declined to answer questions about the incident at a hustings event in Birmingham, in central England, on Saturday, saying that the audience wanted instead to hear about his plans for Britain three years after the country voted to leave the European Union.
International Trade Secretary Liam Fox, who is backing Hunt, agreed the reports should not distract from important policy debate in the race to become the next prime minister which will be decided by 160,000 Conservative party members next month.
“I think it’s always easier to just give an explanation,” he told the BBC’s Andrew Marr on Sunday.
“But the key thing then is how you get on to the issues; what we can’t have is it being a distraction from explanations about wider polices and where we go to and when.”
The clear favorite, Johnson had tried to stay out of the limelight, and opponents have accused him of running from scrutiny to avoid the gaffes that have been a feature of his career so far.
LOUD ALTERCATION
Polling for the Mail on Sunday newspaper showed Johnson was seen as the best prime minister by 36% of all voters on Thursday, while Jeremy Hunt was supported by 28%.
But Johnson had lost the lead on Saturday, with 32% supporting Hunt and 29% Johnson.
Among Conservative voters, Johnson’s lead fell from 55% to 45%, while Hunt’s standing rose from 28% to 34%, the polls conducted by Survation showed.
Police were called to an address in south London where Johnson is living with girlfriend Carrie Symonds in the early hours of Friday morning after neighbors heard a loud altercation. Johnson, 55, is currently divorcing his second wife.
All occupants of the address were spoken to and were all safe and well, police said in a statement.
Johnson supporters have said the action of a neighbor in releasing a recording of the row to the Guardian newspaper was politically motivated.
Neighbor Tom Penn, 29, said in a statement he had called the police because he was “frightened and concerned for the welfare of those involved”.
“Once clear that no one was harmed, I contacted the Guardian, as I felt it was of important public interest,” he said. “I believe it is reasonable for someone who is likely to become our next prime minister to be held accountable for all of their words, actions and behaviors.”
Penn said voted to remain the European Union three years ago, but that was the extent of his involvement in politics.
Johnson, who has a leading Brexit campaigner in the 2016 referendum, on Saturday reiterated his desire to leave the European Union in October with or without a deal.
Hunt, who backed Remain in the referendum, said he would take the country out of the EU without a deal on Oct. 31 if the EU had not showed it was willing to renegotiate the Brexit deal.
LONDON — Police were called to the home of Boris Johnson on Friday after a report from a neighbor of the man who looks poised to become Britain's next prime minister.
London's Metropolitan Police said in a statement they received a call just after midnight local time Friday from a resident who "was concerned for the welfare of a female neighbor."
They attended a home in the south London area where Johnson lives with partner Carrie Symonds, but said the residents of the home in question were found to be "safe and well."
"There were no offences or concerns apparent to the officers and there was no cause for police action," the statement added.
A neighbor told the U.K. newspaper The Guardian they had called police after hearing a woman scream followed by "slamming and banging."
The Guardian claims an audio recording of the altercation by the neighbor reveals Symonds yelling at Johnson to leave the flat, which he refused, followed by a crashing sound.
Symonds is heard saying Johnson had ruined a sofa with red wine, according to the Guardian's account.
"You just don’t care for anything because you’re spoilt. You have no care for money or anything," Symonds is quoted as saying by the newspaper.
NBC News could not independently obtain the recording or verify its contents.
A spokesperson for Johnson didn't immediately respond to a request for comment.
Johnson is one of two remaining candidates competing to lead Britain's ruling Conservative Party after Prime Minister Theresa May stepped down as its leader earlier this month.
By a quirk of the U.K.'s political system, that person will also become the next prime minister — no general election is needed.
Johnson begins his campaign to win over the party's membership on Saturday.
The New York-born former mayor of London and foreign secretary enters the final stage of the contest as the clear favorite against current foreign secretary Jeremy Hunt.
Eight other leadership hopefuls were eliminated in earlier rounds of voting among the party's Members of Parliament, with Johnson holding commanding leads in each round.
The two remaining candidates will now travel the country to make their case to the 120,000 voters who will decide their fate.
Party members will begin the final vote for the new leader next month with results slated to be announced July 22.
Whoever wins will be handed the responsibility of navigating Brexit ahead of the U.K.'s Oct. 31 deadline to leave the European Union.
Johnson has vowed to stick to that deadline — even if no deal has been agreed.
Linda Givetash
Linda Givetash is a reporter based in London. She previously worked for The Canadian Press in Vancouver and Nation Media in Uganda.
The Home Office did not comment but has previously said it would try to block IS recruits hoping to return to the UK.
The interview is the fullest account yet of the Briton's time with IS in Syria, and Jack Letts said he was not speaking under duress.
Dubbed "Jihadi Jack" by the media, he converted to Islam aged 16.
Two years later, in 2014, he dropped out of studying for his A-levels at a school in Oxford, moved to Syria and joined IS - the jihadist terror group which became known worldwide for its brutal mass killings and beheadings.
He married a woman whose family were influential in the group in Fallujah, Iraq. He had a child, who he has never seen.
In 2017 he left IS, but was captured and is in a Kurdish-run jail in northern Syria.
The Briton, who has not been stripped of his UK citizenship and is a dual Canadian national, agreed to speak to the BBC, saying he wanted to come clean about his role in IS.
'I did what I did'
Reporter Quentin Sommerville, who interviewed the IS recruit while Kurdish security forces were present, said there were gaps in his story.
Challenged on whether he was a traitor, the IS fighter replied: "I know I was definitely an enemy of Britain.
"I did what I did," he added. "I made a big mistake, and that's what happened."
Pressed on why he abandoned the UK to join the jihadist group - which has carried out terror attacks across the world - he said: "I thought I was leaving something behind and going to something better."
He said his home life had been comfortable, adding: "I had a very good relationship with my mum, especially, and my dad as well, actually.
"I used to work with my dad. He was a farmer... I used to love actually working with him. I had a very good relationship."
He said he thinks the decision to travel to Syria was a "weird combination of thoughts" and "weird sort of confusion".
"I thought it was some sort of morality actually at the time," he said. "Why do I have this nice life, and others don't? And then, on top of that, the idea of it being an Islamic state and it's actually your duty to do this.
"I think it was probably just a very emotionally-driven period of my life. I'm just glad that I didn't die."
'I wouldn't give me a second chance'
The former IS member said the group used to "encourage you in a sort of indirect way" to put on a suicide vest. He said he made it obvious to militants that "if there was a battle, I'm ready".
"I used to want to at one point, believe it or not" he added. "Not a vest. I wanted to do it in a car. I said if there's a chance, I will do it."
He said he now believes suicide attacks are "haram"- meaning forbidden in Islamic law.
He said at the start he loved living in Raqqa. He fought on the frontlines and was badly injured in Iraq.
One of the main reasons he left IS, he said, was because they started to kill people who he knew were Muslims.
"I didn't have a full plan. I thought I'd just get to Turkey and ring my mum, and just be like, 'I want to meet you somehow'."
'Poster boy'
His parents, John Letts, 58, and Sally Lane, 57, faced trial, accused of sending or trying to send their son money after he had joined IS.
On Friday, they were found guilty of one charge of funding terrorism by sending £223 in 2015. They were cleared of sending him a further £1,000 and the jury could not reach a verdict on a third charge related to an attempt to send £500.
When told that there was very little appetite in the UK to give him a second chance, Mr Letts said: "It's not like I'm appealing to the British public to give me a second chance.
"If I was a member of the British public, I wouldn't give me a second chance probably."
Challenged that his recruitment to IS - as a Westerner who travelled from Britain - was a rallying cry for the terror group, he said he realised it "had more meaning" than for a Syrian recruit, and added that IS used him as a sort of "poster boy".
"The fact that I came from England, et cetera, I understand that it made a big difference."
Although admitting he fought for IS, he said he did not believe he killed anyone.
As a dual national, he has been in touch with Canadian authorities and they are believed to be considering allowing him to leave Syria for Canada.
The Home Office did not comment on the case, but believes that anyone who travels to Syria is putting themselves in danger and could pose a national security risk to the UK.
Home Secretary Sajid Javid has previously said he would "not hesitate" to prevent the return of people who travelled to support IS.
In an interview with the Times, Mr Javid said that a range of measures were available to "stop people who pose a serious threat from returning to the UK, including depriving them of their British citizenship or excluding them from the country".
