Tensions between the US and North Korea hit new highs overnight after US President Donald Trump said he would retaliate to any escalation with "fire and fury".
The North Koreans have responded by saying on state media that they are "carefully examining" a missile attack on Guam, a US base in the Pacific.
Pyongyang said it was considering using "enveloping fire" in the area, where US strategic bombers are held, using its medium-to-long range Hwasong-12 missiles. The US has been carrying out military drills in Guam recently.
The Korean People's Army (KPA) said the US bombers "threaten and blackmail [North Korea] through their frequent visits to the sky above South Korea".
"It is a daydream for the US to think that its mainland in an invulnerable heavenly kingdom," the KPA said.
The most recent spike in rhetoric follows two missile tests in North Korea in July. North Korean leader Kim Jong-Un trialled intercontinental ballistic missiles, and said they had the ability to strike in mainland US.
Media reports in the US have said North Korea has now manufactured a nuclear warhead small enough to fit inside the missiles.