SEOUL — The U.S. and South Korea launched a five-day anti-submarine drill Monday in the West Sea, site of past clashes between the two Koreas, according to South Korea’s Ministry of National Defense.

South Korean officials would not say whether the exercise is being conducted near the Northern Limit Line, the maritime border between the two Koreas, or how many troops and vessels from each nation are participating.

However, Yonhap reported that a nuclear-powered aircraft carrier would be involved, along with Aegis destroyers from both nations, P-3C patrol aircraft and submarines.

A spokesman for South Korea’s Joint Chiefs of Staff on Monday described the drill as a routine defensive exercise.

“We are not trying to deliver any message to North Korea with this exercise,” a spokesman for the Joint Chiefs of Staff said. “This exercise is for improving the U.S.-South Korean warfighting power.”

The North is believed to have torpedoed a South Korean patrol ship in March 2010 in the West Sea near one of South Korea’s border islands, and in November 2010 shelled the South’s Yeonpyeong Island, killing four people, including two civilians.

The naval drill comes a week after the U.S. and South Korea ended their annual joint Foal Eagle exercise following a period of increasingly bellicose threats from North Korea that included a vow to turn Seoul and Washington, D.C., into a “sea of fire.” Pyongyang also said its military had the go-ahead to use nuclear weapons on American interests, and declared void the armistice that ended the Korean War.

North Korea also withdrew its workers from the jointly run Kaesong Industrial Complex and prohibited South Korean workers from entering the factory compound that was the lone remaining symbol of inter-Korean cooperation, as well as a source of income for the impoverished North.

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