North Korean leader Kim Jong-un has told his generals to put rocket units on standby and prepare for an attack on the US, the nation's state media has reported.
Kim Jong-un said the time had come to "settle accounts with US imperialists" after a late night meeting with top generals, according to state news agency KCNA,
He ordered rockets "to be on stand-by for fire so that they may strike any time", the KCNA report said.
"If they make a reckless provocation with huge strategic forces, the Korean People's Army (KPA) should mercilessly strike the US mainland, their stronghold, their military bases in the operational theatres in the Pacific, including Hawaii and Guam, and those in South Korea," the report quoted him as saying.
According to the Associated Press news agency, thousands of North Koreans then attended a rally in the capital to show their support for Kim Jong-un.
Yonhap news agency quoted an unidentified military official who said increased activity had been noted at North Korea's missile sites.
The move comes after two US stealth bombers flew over the Korean peninsula in annual US and South Korean military drills.
"This demonstrates the United States' ability to conduct long range, precision strikes quickly and at will," the US military said in a statement.
"The B-2 bomber is an important element of America's enduring and robust extended deterrence capability in the Asia-Pacific region."
North Korea has made repeated threats on the US and South Korea since a fresh wave of UN sanctions were imposed in response to the nation's third nuclear test blast.
The sanctions, voted on by the UN Security Council earlier in March, target North Korea's ruling class and place bans on countries exporting luxury good to the communist state, including jewellery, yachts and luxury cars, as well as tightening financial restrictions.
North Korea responded to the sanctions by “ending” the armistice with South Korea signed at the end of the 1953 conflict, shutting its shared border and closing its hotline with Seoul.
It also warned of a pre-emptive strike against "aggressors" and pledged to retaliate with "crushing strikes" to anyone who dared trespass onto their territory
At the time experts pointed out Pyongyang had a history of such rhetoric and while the US said it was taking the threats seriously they added they were "not unusual."