North Korean leader Kim Jong-Un has warned that his rocket forces are ready "to settle accounts with the US".
The new onslaught comes after US nuclear-capable B-2 bombers dropped dummy munitions in joint military drills with South Korea.
Kim's warning, and the litany of threats that have preceded it, don't indicate an imminent war.
In fact, they're most likely meant to coerce South Korea into softening its policies, win direct talks and aid from Washington, and strengthen the young leader's credentials and image at home.
But the threats from North Korea and rising animosity from the rivals that have followed UN sanctions over Pyongyang's February 12 nuclear test do raise worries of a misjudgment leading to a clash.
Kim "convened an urgent operation meeting" of senior generals just after midnight, signed a rocket preparation plan and ordered his forces on standby to strike the US mainland, South Korea, Guam and Hawaii, state media reported.
Later yesterday at the main square in Pyongyang, tens of thousands of North Koreans turned out for a 90-minute mass rally in support of Kim's call to arms.
South Korea said it was mindful of the possibility that North Korean drills could lead to an actual provocation.
It also said it is watching or any signs of missile launch preparations in North Korea.