South Korea's military Monday launched a computer-simulated war game against North Korea amid tensions over the communist state's missile and nuclear tests, officials said.

The North regularly denounces such exercises as preparations for an invasion.

Seoul's Joint Chiefs of Staff said the four-day Taegeuk exercise, which began on schedule Monday, is defensive in nature and involves only the command posts of South Korea's army, naval and air force.

The annual drill began in 1995.

The South's 655,000-strong military, backed up by a 28,500-strong US contingent, faces off against the North's 1.2 million-member armed forces.

Inter-Korean relations have been frosty for over a year. The North is also locked in a fresh standoff with the international community over its banned nuclear and ballistic missile programmes.

After the United Nations Security Council censured its April 5 long-range rocket launch, the North announced it was quitting six-party nuclear disarmament talks.

It staged its second nuclear test on May 25, prompting the Council to adopt a new resolution imposing tougher sanctions.