U.S. and South Korean forces kicked off annual computer-simulated military exercises Monday that North Korea routinely criticizes as a rehearsal for an imminent invasion of the communist state.

About 10,000 U.S. troops are participating in the drills, dubbed Ulchi Focus Lens 2005, said U.S. military spokesman David Oten (search).

The exercises, scheduled to last until Sept. 2, are designed to evaluate and improve coordination for conducting defense operations on the Korean Peninsula, the U.S. military said in a statement.

Oten said about half of the U.S. troops were participating from bases outside South Korea. The number of South Korean forces taking part wasn't immediately available.

This year's drills come at a sensitive time, a week ahead of the scheduled resumption of international talks aimed at persuading North Korea to give up its nuclear program and amid burgeoning economic and political exchanges between the two Koreas.

The participants in the multinational talks -- China, Japan, North Korea, Russia, South Korea and the United States -- met for nearly two weeks in Beijing in late July and early August and are set to reconvene next week in the Chinese capital.

The negotiations stalled over the issue of whether North Korea can have nuclear power for "peaceful" purposes such as energy generation. The United States says Pyongyang must have no access to nuclear power.

North Korea regularly blasts the Ulchi Focus drills, accusing the United States of planning to launch an invasion of its territory. It also says Washington is preventing the two Koreas from achieving unification.

North Korea characterized this year's exercises as "fraught with greater danger of invasion as they are scheduled to take place at a time when the U.S. war preparations have reached their final phase," the official Korean Central News Agency (search) said Saturday.

Relations between North and South Korea have warmed since a historic summit between their leaders in 2000. The have established a joint industrial zone in North Korea and regularly carry out talks on a variety of issues.

About 32,500 U.S. troops are stationed in South Korea as a legacy of the 1950-53 war, which ended in a cease-fire, leaving the two Koreas still technically at war.