S. Korea launches naval drills in Yellow Sea

South Korean troops fired artillery and dropped sonar buoys into the Yellow Sea as naval drills kicked off Thursday near the spot where a warship sank in March.

Some 4,500 South Korean troops aboard more than 20 ships and submarines as well as about 50 aircraft were to take part in the five days of naval exercises off the west coast, including spots near the two Koreas' maritime border, the Joint Chiefs of Staff said.

North Korea called the drills a military provocation that threatened to reignite war on the Korean Peninsula. The Committee for the Peaceful Reunification of the Fatherland called it proof that the South was preparing to invade, according to a statement carried by North Korea's official Korean Central News Agency.

The drills come just weeks after South Korea's joint military exercises with the U.S. off the east coast manoeuvres held in response to the deadly March sinking of the Cheonan warship, which killed 46 South Korean sailors.

A five-nation team of investigators concluded in May that a North Korean torpedo fired from a submarine sank the 1,200-tonne Cheonan as the warship was carrying out routine surveillance. North Korea denied sinking the ship.

Disputed border

The waters off the west coast have been the site of several naval clashes between the two Koreas. The three-year Korean War ended in an armistice in 1953, but North Korea disputes the western maritime border unilaterally drawn by the United Nations.

North and South have engaged in three bloody battles near the line, most recently in November 2009, and the Cheonan went down in March not too far from the border.

Pyongyang warned earlier in the week that it would "counter the reckless naval firing projected by the group of traitors with strong physical retaliation and advised civilian ships to stay away from the maritime border.

The North also threatened to respond to last month's South Korea-U.S. military exercises with "nuclear deterrence" but South Korean military officials said there was no sign of unusual North Korean military activity.

North Korea routinely issues such threats, especially when the South holds joint military drills with the U.S. Pyongyang sees the exercises as a rehearsal for an invasion. The U.S. has 28,500 troops in South Korea to protect the longtime Asian ally.

South Korea was closely monitoring North Korea's military but spotted no unusual activity Thursday, the Joint Chiefs of Staff said.