The United States and South Korea have launched their large-scale military drills in the Sea of Japan, a move that is feared may further complicate the security situation in the region. The drills, code-named "Invincible Spirit", will run until Wednesday.

The war games involve the Nimitz-class aircraft carrier USS George Washington, 20 ships and submarines and 200 aircraft, with about 8-thousand troops on board.

Four Japanese military observers are on board the carrier. US military officials say the maneuvers are intended to send a strong signal to the Democratic People's Republic of Korea that aggression in the region will not be tolerated. But analysts say the scale of the war games are much larger than previously agreed by the two countries.

This is the first in a series of joint drills off South Korea's east coast. The DPRK has threatened a military response to the exercises as tension remains high on the peninsular following the sinking of a South Korean warship earlier this year.

Similar exercises are also scheduled to take place in the Yellow Sea, in international waters closer to China's shores.