North Korea says it has ordered artillery and rocket units into «combat posture» to prepare to target US bases in Hawaii, Guam and the US mainland.
The announcement, carried by KCNA news agency, follows days of strong rhetoric from Pyongyang.
The Pentagon condemned the threats, saying the US was ready to respond to «any contingency».
South Korea on Tuesday marked the third anniversary of the sinking of the Cheonan ship, in which 46 sailors died.
It said there was no unusual activity in the North.
Tensions remain high on the Korean peninsula in the wake of North Korea’s third nuclear test on 12 February. The test led to new UN sanctions which Pyongyang strongly opposes.