North Korea says its armed forces are at full combat readiness in response to the start of annual military exercises by US and South Korean troops.
In a statement read on state television, a military official warned that any attempt to shoot down the long-range missile North Korea plans to launch soon would be seen as an act of war.
Pyongyang routinely accuses the US and South Korea of aggressive intentions with the military exercises, but its rhetoric this time has been more strident.
It called the drills a provocation that would only occur ‘on the eve of a war’, and threatened to cut off its hotline with the South's military - the one telephone link between the two armies who are massed on either side of the border.
US marines will conduct live-fire drills north of Seoul and within an hour's drive from the border. A US aircraft carrier will take part in the exercises.
The drills come as Pyongyang prepares to test-fire its Taepodong-2 missile.
Pyongyang says the launch would be for a satellite as part of its communications development, though under UN sanctions it is barred from firing a ballistic missile.
Japan, the US and South Korea have said they see no difference between a satellite and a missile launch because they use the same technology and the same rocket.
In Seoul, the new US special envoy for North Korea, Stephen Bosworth, held talks with South Korean officials on how to restart negotiations on ending the North's nuclear arms programme.
The two Koreas are technically still at war and station about 1m troops near their respective sides of the Demilitarised Zone that has divided the peninsula since the 1950-53 Korean War ended in a ceasefire - but not a peace treaty.
