SEOUL: North Korea said Tuesday it would strengthen its nuclear deterrent in response to US military threats and is prepared for both dialogue and war with Washington.

The comments from a foreign ministry spokesman follow Monday's launch of a major US and South Korean military exercise which the North depicts as a rehearsal for invasion.

On Monday the communist state said it had ordered its military on full alert and announced readiness to "blow up" South Korean facilities.

The US and South Korea say the annual Key Resolve/Foal Eagle exercise, which involves 18,000 American and 20,000 South Korean troops, is defensive.

North Korea habitually responds angrily to the war games south of the border but they normally pass off without major incident.

This year's exercise coincides with diplomatic efforts to bring the North back to six-nation nuclear disarmament talks. The North quit the forum last April, a month before staging its second atomic weapons test.

As a precondition for returning, it demands a US commitment to open talks about a peace treaty to replace the armistice which ended the 1950-53 Korean War.

The ministry spokesman, quoted by Pyongyang's official news agency, described the military drill as "nuclear war exercises aimed at mounting a preemptive attack" on the North.

The exercise proved the justice of the proposal for a peace treaty, the spokesman added.

"The DPRK (North Korea) is fully ready for dialogue and war. It will continue bolstering up its nuclear deterrent as long as the US military threats and provocations go on."