North Korean leader Kim Jong Un said his rocket forces are ready "to settle accounts with the US", escalating the country's bellicose rhetoric and responding directly to the unprecedented announcement that nuclear-capable US B-2 bombers had joined military drills with South Korea.
Mr Kim's comments, made in a meeting with his senior generals, are part of a rising tide of threats meant to highlight anger over the military drills and recent United Nations sanctions over Pyongyang's nuclear test.
North Korea sees US nuclear firepower as a direct threat to its existence and claims the annual military drills are a preparation for invasion.
Pyongyang also uses the US nuclear arsenal as a justification for its own push for nuclear-tipped missiles that can strike the United States - a goal that experts believe to be years away, despite a nuclear test last month and a long-range rocket launch in December.
A full-blown North Korean attack is unlikely, though there are fears of a more localised conflict such as a naval skirmish in disputed Yellow Sea waters. Such naval clashes have happened three times since 1999.
North Korea's threats are seen by outside analysts as efforts to provoke South Korea to soften its policies and to win direct talks with Washington that could result in aid. Kim's comments are also seen as ways to build domestic loyalty and strengthen his military credentials.
State media said Kim met his senior generals, signed a rocket preparation plan and ordered his forces on standby to strike the US mainland, South Korea, Guam and Hawaii. Many analysts say they have seen no evidence that Pyongyang's missiles can hit the US mainland. But it has capable short- and mid-range missiles, and Seoul is only a short drive from the heavily armed border separating the Koreas.
US Forces Korea said the B-2 stealth bombers flew from a US air base in Missouri and dropped dummy munitions on the South Korean island range before returning home.
The statement follows an earlier US announcement that nuclear-capable B-52 bombers participated in the joint military drills. Defence Secretary Chuck Hagel said the decision to send B-2 bombers to join the military drills was part of normal exercises and not intended to provoke North Korea. He acknowledged, however, that North Korea's belligerent tones and actions in recent weeks had ratcheted up the danger in the region "and we have to understand that reality".
Meanwhile, thousands turned out for a mass rally at the main square in Pyongyang in support of their leader's call to arms. Chanting "Death to the US imperialists" and "Sweep away the US aggressors", soldiers and students marched through Kim Il Sung Square during the 90-minute rally.