South Korean and U.S. troops have begun annual military drills that North Korea warned could trigger a nuclear war on the divided peninsula.
About 13,000 U.S. troops and some 200,000 South Korean soldiers are to participate in the drills, which are aimed at defending South Korea and responding to any attack.
The main part of the drills, which will involve computer war games and live-firing exercises, will last 11 days, while some field training will continue until late April, according to the South Korea-U.S. joint forces command in Seoul.
U.S. State Department spokesman P.J. Crowley said that North Korea had been informed on February 14 about the exercises, which he said were routine. He told a news conference in Washington that North Korea's "belligerent rhetoric” is unwarranted.