North Korea announced that it is considering an attack on the United States territory of Guam.
The official news agency of the communist nation said on Tuesday the plan involved firing medium-to-long-range rockets at Guam, where US strategic bombers are based.
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 threatened the North with “fire and fury” on Tuesday.
Tillerson said that North Korean dictator 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”.
The recent exchanges mark a sharp rise in threats between Washington and Pyongyang, but China has remained peaceful.
A foreign ministry statement reported by Reuters called on all sides to avoid words or actions which might escalate the situation.
The UN recently approved further economic sanctions on North Korea, which Pyongyang said were a “violent violation of our sovereignty”, warning the US would “pay a price”.
On Wednesday, the official KCNA news agency said North Korea was “carefully examining the operational plan for making an enveloping fire at the areas around Guam” using its medium-to-long-range Hwasong-12 missiles.
The news agency reported a military statement issued on Tuesday, which likely came in response to US military drills in Guam.
However, there has been no indication that any attack on Guam by North Korea is imminent.
In a message to the public, the governor of Guam Eddie Baza Calvo said there was currently “no threat” to the island and the Marianas archipelago, but that Guam was “prepared for any eventuality”.