Defence Secretary James Mattis has said the US is not looking for the "total annihilation" of North Korea, but stressed that there were "many options" in how to respond to Pyongyang's latest nuclear bomb test.
Mr Mattis said Donald Trump met with a small group of military and defence officials at the White House after US intelligence officials confirmed that the test of a bomb that is reportedly ready to fit onto an intercontinental ballistic missile (ICBM).
"We made it clear we have the ability to defend ourselves and our allies," Mr Mattis said.
Mr Mattis said North Korea's leader Kim Jong-un should "take heed" of the United Nations Security Council's "unified voice" on the issue, as shown by its decision to impose sanctions as well as its "commitment to denuclearise the Korean peninsula".
The Defence Secretary also stressed the "iron-clad" commitments of the US to allies like South Korea and Japan.
"Any threat to the US", its territories like the Pacific island of Guam, or its allies would be met with a "massive military response ... both effective and overwhelming," Mr Mattis said.
He said the group of military advisers had briefed the President on each of the military responses available.
Mr Trump has previously made it known that "all options are on the table" with regards to North Korea, raising fears of war. And, as he left church on Sunday morning, he said simply "we'll see" when asked by a reporter if military action would be taken.
Mr Mattis, however, has said that the US will never run out of diplomatic solutions, implying that military action against Mr Kim would be a last resort.
A few months ago, it was reported that North Korea had developed the technology to fit a nuclear warhead capable of fitting on an ICBM.
A week ago, Pyongyang fired a missile over the Japanese island of Hokkiado and then came the test of what North Korea said was an advanced hydrogen bomb.
UN Secretary General Antonio Guterres said the latest test was "profoundly destabilising for regional security".
The US Ambassador to the UN, Nikki Haley, confirmed the Security Council would hold an emergency meeting on Monday to discuss the situation at the request of France, Japan, South Korea, the UK, and the US.
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