0129 GMT October 21, 2017
North Korea said it was "carefully examining" a plan to strike Guam, which is home to about 163,000 people and a US military base that includes a submarine squadron, an airbase and a Coast Guard group, Reuters reported.
A Korean People's Army spokesman said in a statement that the plan would be put into practice at any moment, once Leader Kim Jong-un made a decision.
Guam Governor Eddie Calvo dismissed the threat and said the island was prepared for "any eventuality" with strategically placed defenses. He said he had been in touch with the White House and there was no change in the threat level.
North Korea also accused the United States of devising a "preventive war" and said in another statement that any plans to execute this would be met with an "all-out war, wiping out all the strongholds of enemies, including the US mainland".
Washington has warned it is ready to use force if needed to stop North Korea's ballistic missile and nuclear programs but that it prefers global diplomatic action, including sanctions. The UN Security Council unanimously imposed new sanctions on North Korea on Saturday.
Trump issued his strongest warning yet for North Korea in comments to reporters in New Jersey on Tuesday.
"North Korea best not make any more threats to the United States. They will be met with fire and fury like the world has never seen," Trump said.
US Secretary of State Rex Tillerson, before landing in Guam on a pre-arranged visit, said Trump was trying to send a strong message.
Just moments after Tillerson's remarks were reported, Trump hammered home his tough talk in a Twitter post about the US nuclear arsenal, in what looked like another warning to North Korea.
"My first order as President was to renovate and modernize our nuclear arsenal," he said. "It is now far stronger and more powerful than ever before."
China, North Korea's closest ally despite Beijing's anger at Pyongyang's missile and nuclear programs, described the situation as "complex and sensitive", and urged calm and a return to talks.
"China calls on all sides to uphold the main direction of a political resolution to the Korean peninsula nuclear issue, and avoid any words or actions that may intensify the problem and escalate the situation," it said in a statement.
Pyongyang says its intercontinental ballistic missiles (ICBMs) are a legitimate means of defense against perceived US hostility, including joint military drills with South Korea.