Theresa May would be prepared to launch a pre-emptive nuclear strike against the UK's enemies, the Defence Secretary said as he branded Jeremy Corbyn a security risk.

Sir Michael Fallon attacked the Labour leader for calling into question Labour's commitment to the Trident nuclear deterrent, and for suggesting he would be reluctant to authorise a drone strike on the leader of the Islamic State terror group.

The Defence Secretary said the Government could not rule out the use of nuclear weapons in a first strike in "extreme circumstances".

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Sir Michael used a series of broadcast interviews to criticise Mr Corbyn's approach to defence policy.

On BBC One's Andrew Marr Show on Sunday, Mr Corbyn , who has previously said he would never authorise the use of nuclear weapons, said he stood by his past views on the subject.

"I have made clear my views on nuclear weapons. I have made clear there would be no first use of it. I have made clear that any use of it would be a disaster for the whole world," he said.

Sir Michael said the Government could not rule out ordering a nuclear first strike.

He told the Today programme: "In the most extreme circumstances we have made it very clear that you can't rule out the use of nuclear weapons as a first strike."

Asked about Sir Michael's comments on a pre-emptive strike, the Prime Minister's official spokesman said there was "no reason to disagree with what the Defence Secretary said".

Sir Michael claimed a victory for Labour in the general election would result in "very dangerous chaos".

He told ITV's Good Morning Britain: "I think you saw Jeremy Corbyn yesterday questioning strikes against terrorists, refusing to back the nuclear deterrent, he's been querying our Nato deployment and he seems to have fallen out with his own party over the nuclear deterrent.

"That's chaos, but it's very dangerous chaos that would put the security of our country at risk."

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Labour was forced to restate its commitment to Trident renewal since Mr Corbyn used the Marr interview to say he would order an immediate strategic defence review looking at "all aspects" of defence policy if he was prime minister after June 8.

Echoing a statement from a party spokesman issued after the interview, Labour campaign chairman Andrew Gwynne said renewal of Trident would be in the party's manifesto.

"Yes, it's Labour Party policy. We are committed to renewing the Trident system," he told BBC Radio 4's Today programme.

Sir Michael's comments signalled that the Tories intend to make Mr Corbyn's suitability for high office a key issue in the general election campaign.

But he was unable to stamp out questions over whether Theresa May will recommit to David Cameron's pledge not to put up income tax, VAT or national insurance.

The Defence Secretary left the door open to tax rises, admitting the Tories do not want to commit to too many "prescriptive" targets in its general election manifesto.

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Shadow defence secretary Nia Griffith said she had made it clear to Mr Corbyn that the party supported the nuclear deterrent.

"It absolutely will be in the manifesto because it's firmly our policy, and that's been reaffirmed time after time," she told BBC Two's Daily Politics.

Challenged on Mr Corbyn's position on authorising a nuclear strike, Ms Griffith said it was "very important that we are absolutely clear that we are prepared to use it".

She said the option of force and the "ultimate deterrent" meant "you are far more likely to actually sustain peace and security at the end of the day".