North Korea has conducted its sixth and most powerful nuclear test, which it says is was of an advanced hydrogen bomb for a long-range missile, prompting the threat of a "massive" military response from the US if it or its allies are threatened.
Speaking outside the White House after meeting with President Donald Trump and his national security team, US Defense Secretary Jim Mattis said Trump asked to be briefed on all available military options.
"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," Mattis said.
"We are not looking to the total annihilation of a country, namely North Korea," Mattis said with Joseph Dunford, the chairman of the Joint Chiefs of Staff, at his side. "But as I said, we have many options to do so."
Trump earlier in the day refused to rule out military action and threatened to cut off trade with any country doing business with Pyongyang.
Asked while leaving a church service whether the US would attack North Korea, Trump replied: "We'll see."
The United Nations Security Council is scheduled to meet on Monday to discuss the nuclear test. Mattis said the members of the council "remain unanimous in their commitment to denuclearisation of the Korean Peninsula."
In a series of early morning tweets, the president also appeared to rebuke ally South Korea, which faces an existential threat from North Korea's nuclear program.
"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!" Trump said in an early morning tweet.
Trump appeared to be blaming South Korea for a policy it abandoned years ago of trying to soften North Korea's posture through economic aid.
Reports that the United States is considering pulling out of its trade deal with South Korea has also ratcheted up tensions with the country.
A former senior State Department official criticised Trump for accusing South Korea of appeasement.
"It was unseemly, unhelpful, and divisive to gratuitously slap our major ally at the very moment when the threat from (North Korea) has reached a new height," said the official, who spoke on condition of anonymity.
North Korea, which carries out its nuclear and missile programs in defiance of UN Security Council resolutions and sanctions, said on state television that the hydrogen bomb test ordered by leader Kim Jong Un had been a "perfect success."
The bomb was designed to be mounted on its newly developed intercontinental ballistic missile, or ICBM, the North said.
The test had registered with international seismic agencies as a man-made earthquake near a test site. Japanese and South Korean officials said the tremor was about 10 times more powerful than the one picked up after North Korea's last nuclear test a year ago.
After weeks of profound tensions over North Korea's nuclear program, the size and scope of the latest test has set off a new round of diplomatic handwringing.
Chinese President Xi Jinping and Russian President Vladimir Putin, who met on the sidelines of a BRICS summit in China, agreed to "appropriately deal" with North Korea's nuclear test, the Xinhua news agency reported.
As North Korea's sole major ally, China said it strongly condemned the nuclear test and urged Pyongyang to stop its "wrong" actions.
Hours before the test, Trump talked by phone with Japanese Prime Minister Shinzo Abe about the "escalating" nuclear crisis in the region.