The United Nations Security Council will hold an emergency meeting in response to North Korea's most powerful nuclear test - as the Trump administration warned any threat to the US or its allies would trigger a "massive military response".
Today's meeting, at the request of the UK, US, Japan, France and South Korea, comes after Kim Jong Un's regime carried out its sixth test of a nuclear device.
US Defence Secretary Jim Mattis briefed President Donald Trump about the military options available if the crisis escalated, adding that Washington was capable of launching an "effective and overwhelming" response. While the US was "not looking to the total annihilation" of North Korea there were "many options to do so", he said.
But in the UK Foreign Secretary Boris Johnson cautioned against a military strike, because North Korea already had the ability to "vaporise" large parts of the population of South Korea, even without nuclear weapons.
Prime Minister Theresa May said Pyongyang's actions posed an "unacceptable further threat to the international community" and urged world leaders to increase pressure on the regime.
The test blast came after propaganda pictures were published of Kim examining what was said to be a nuclear warhead being fitted on to the nose of an intercontinental ballistic missile.
Mrs May reiterated the call for "tougher action, including increasing the pace of implementation of existing sanctions and looking urgently in the UN Security Council at new measures" she had made alongside Japanese Prime Minister Shinzo Abe during her visit last week. She said: "This is now even more pressing. The international community has universally condemned this test and must come together to continue to increase the pressure on North Korea's leaders to stop their destabilising actions."
Mr Trump branded North Korea "a rogue nation" and indicated that he was considering a trade boycott of nations that dealt with North Korea - widely viewed as a reference to China, although commentators questioned how the US would be able to take such a step.
The Foreign Secretary played down the prospect of military action, although he acknowledged all options remained on the table.
Mr Johnson said: "There is no question that this is another provocation, it is reckless, what they are doing is, they seem to be moving closer towards a hydrogen bomb which, if fitted to a successful missile, would unquestionably present a new order of threat."
Arguing for a diplomatic solution he said: "It's certainly our view that none of the military options are good.
"It is of course right to say that all options are on the table, but we really don't see an easy military solution."
The Chinese government "expressed firm opposition and strong condemnation" and urged North Korea to "stop taking erroneous actions that deteriorate the situation".