The annual Ulchi Focus Lens Exercise involves computerised war simulations and 14,500 US troops based in and out of South Korea, said US military officials in Seoul.

Seoul’s Defence Ministry gave no exact figures on South Korean troops participating in the 12-day exercise, but confirmed it was the biggest joint military manoeuvre with the United States.

North Korea has blasted the war games with Pyongyang’s Foreign Ministry calling them preparations for a “pre-emptive attack” on the Communist country.

Washington and Pyongyang have been locked in a 10-month standoff over North Korea’s nuclear weapons development drive.

The United States, China, Russia, Japan and the two Koreas have agreed to hold six-party talks in Beijing from 27-29 August to address the nuclear crisis after weeks of wrangling over a dialogue format.

The United States has about 37,000 troops stationed in South Korea as part of a Mutual Defence Treaty signed after the 1950-1953 Korean war.

The two Koreas remain technically at war since the conflict which ended in an armistice, rather than a peace treaty.