Nuclear weapons should be negotiated away “as quickly as possible”, Jeremy Corbyn said.
The Labour leader acknowledged that the party’s policy was for multilateral disarmament but insisted he would be “totally on the case” working for a world free of nuclear weapons.
Mr Corbyn said the crisis in North Korea illustrated the danger of nuclear-armed nations and urged Donald Trump and Kim Jong Un to tone down their rhetoric.
In an interview with CNN Mr Corbyn said there had to be a rapid return to the six-party talks process aimed at resolving the Korean crisis.
“I think the tragedy in all this is that Donald Trump and Kim Jong Un have been using sirens to talk to each other. And the language is getting worse and worse and the threats are getting worse and worse.
“I think it’s wholly wrong that North Korea develops nuclear weapons.
“I would hope the UN would ask for cessation of the verbal hostilities and ask the general secretary to speak directly to Trump, directly to Kim Jong Un and try and wind down the rhetoric.
“Because if anybody, anybody fires off any weapon of mass destruction, a nuclear weapon, against anybody, it won’t stop at national borders.
“Listen, I want to live in a world free of nuclear weapons. I support multilateral disarmament. But it has got to be now, it has got to be urgent and it’s got to be, I think, through the UN.”
Pressed on his own nuclear policy, Mr Corbyn said Labour’s manifesto commitment was to “work for a nuclear-free world”.
He continued: “We haven’t written the manifesto for the next election yet. But that was what was in the manifesto in which we just gained nearly 13 million votes. But we’re very clear – very, very clear – that nuclear weapons really must be negotiated away as quickly as possible.
“Look at the danger now with very small-scale nuclear weapons in North Korea. And obviously incredibly powerful nuclear weapons held by the United States.
“We have to wind down the rhetoric quickly. And now and as a member of the Security Council, Britain obviously has a contribution and a part to play in that.”
Mr Corbyn also restated his view that Nato’s commitment to mutual assistance did not necessarily mean providing military support to an ally that had come under attack.
He said: “The Nato charter asks for acts of solidarity and support. It is not necessarily military; it can be diplomatic. It can be economic. It can be a lot of things.”
Mr Corbyn called for dialogue to “de-intensify the stress” on the borders between Nato and Russia.