The US on Sunday threatened North Korea with an overwhelming military response if it attacked American interests or allies in the region following the rogue state’s biggest nuclear test so far.
Donald Trump met his national security advisers in the hours after the underground detonation to be briefed on the range of military options available to him, according to James Mattis, his secretary of defence.
“Any threat to the United States or its territories including Guam or our allies will be met with a massive military response – a response both effective and overwhelming,” said Mr Mattis outside the White House.
His words further ratchet up tension over Kim Jong-un’s rapidly advancing nuclear weapons programme.
On Sunday morning, Pyongyang claimed it had successfully tested a hydrogen bomb which it said could be fitted to its new range of inter-continental ballistic missiles.
Although analysts said they could not verify the claim, they added that the force of the blast suggested North Korea had developed a weapon equivalent to 120 kilotons – an order of magnitude more powerful than the bomb dropped on Nagasaki.
That increased level of danger provoked an increased level of American response.
Mr Mattis warned Kim Jong-un to remember that the world was united against him before delivering the clearest expression yet that America was capable of destroying the North Korean regime.
“We are not looking to the total annihilation of a country, namely North Korea,” he said with Gen Joseph Dunford, chairman of the Joint Chiefs of Staff, standing at his side. “But as I said we have many options to do so.”
Mr Trump has signalled repeatedly that he is ready to use force to stop North Korea’s pursuit of nuclear weapons that could reach the continental US.
But other world leaders talked up diplomatic options on Sunday.
Theresa May, British prime minister, said: “I discussed the serious and grave threat these dangerous and illegal actions present with President Abe in Japan this week and reiterate the call we jointly made for tougher action, including increasing the pace of implementation of existing sanctions and looking urgently in the UN Security Council at new measures.”
The Security Council is expected to meet on Monday morning to address the matter.
However, Mr Trump expressed his frustration with diplomatic manoeuvring and once again refused to rule out the use of force.
As he left a prayer service for Houston flood victims in Washington on Sunday morning, he was asked whether the US would attack North Korea, responding: “We’ll see.”
Earlier he used Twitter to express his impatience with diplomacy.
“North Korea is a rogue nation which has become a great threat and embarrassment to China, which is trying to help but with little success,” he wrote.
“South Korea is finding, as I have told them, that their talk of appeasement with North Korea will not work, they only understand one thing!”
He later floated the idea that the US could halt all trade with nations that did not sever economic links with North Korea.
For now, however, it is talk of military action that dominates the debate.
Pentagon planners have mapped out a suite of military options, ranging from massive nuclear strikes and regime change to pinpoint pre-emptive attacks to destroy missiles before launch.
But that runs the risk of provoking North Korean retaliation against South Korea and American bases, with either conventional or nuclear weapons.
As a result, the latest US threats risk dividing the international alliance facing off against Pyongyang.
Boris Johnson, the British Foreign Secretary, said North Korea had the power to "vaporise" large parts of the population of South Korea even without nuclear weapons.
“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,” he said.
He said it was time for common sense and diplomacy to prevail as he called on China to step up its pressure on its client state. But he summed up North Korea’s rapid progress with a dire warning.
“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,” he said.