The North’s official news agency said on Tuesday the plan involved firing medium-to-long-range rockets at Guam, where US strategic bombers are based, according to the BBC.
US Secretary of State Rex Tillerson, flying into Guam, said there was no imminent threat from North Korea.
He also defended President Donald Trump, who on Tuesday threatened Pyongyang with “fire and fury”.
Tillerson said that North Korean leader Kim Jong-un did not understand diplomatic language, and a strong message was needed that he would understand.
“I think the president just wanted to be clear to the North Korean regime that the US… will defend itself and its allies,” he said.
On Wednesday, President Trump tweeted that the US nuclear arsenal was “more powerful than ever before”, but added he was hopeful “we will never have to use this power”.