North Korea threatened to attack South Korean and U.S. forces for scheduled joint military drills in March even as nuclear envoys picked up the pace of work to get stalled disarmament talks back on track.

South Korea and the United States have held the drills for years without major incident. North Korea regularly criticizes the exercises as a prelude to invasion and nuclear war.

The drills run from March 8 to 18.

A spokesman for the North's army said the military drills by the South and United States troops were nuclear war exercises aimed to preempt a surprise attack on the (North), despite assurance by the two allies that they were purely defensive.

If the U.S. imperialists and South Korean warmongers launch the joint military exercises for aggression, ignoring our repeated warnings, we will react to them with our powerful military counteraction, and if necessary, mercilessly destroy the bulwark of aggression by mobilizing all the offensive and defensive means including nuclear deterrent, the spokesman said.

The threat came as U.S. envoy for North Korea, Stephen Bosworth, held meetings in Seoul trying to push for the restart of talks with the North involving the two countries, Japan, Russia and China to end Pyongyang's nuclear ambitions.

North Korea has boycotted the talks since late 2008 and has demanded a peace treaty with the United States and the suspension of U.N. sanctions imposed after its nuclear test last year.

Washington has said North Korea's demands for aid and improved relations can be addressed only along with renewed nuclear disarmament steps by Pyongyang.

Bosworth said upon arrival in South Korea that he did not have a clear indication of whether or when the North would return to the table.

South Korea's envoy for the six-party talks, Wi Sung-lac, held talks with Bosworth on Thursday after returning from Beijing where he discussed the issue with the host of the six-way talks.

Bosworth goes to Japan on Friday.

(Reporting by Jack Kim; Editing by Nick Macfie)

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