About 20,000 South Korean and US troops launched a 12-day joint military exercise on Monday in South Korea, the Defense Ministry announced.

Except for South Korean troops and the US troops stationing in South Korea, a small number of US soldiers from US military bases in Guam, Japan and other areas also joined the annual drill, dubbed as the "Ulchi Focus Lens", the South Korean Defense Ministry said.

South Korea and the United States began to conduct the "Ulchi Focus Lens" military exercises since 1975. The drill consists mostly of computer-simulated war games to evaluate and improve combined and joint procedures, plans and systems used in the event of conflict on the Korean Peninsula.

North Korea is strongly against the exercise.

About 30,000 US troops are currently stationed in South Korea.

(Xinhua News Agency August 21, 2006)