SEOUL, Aug. 5 (Xinhua) -- South Korea began on Thursday massive anti-submarine drills in waters off the west coast of the divided Korean peninsula despite a warning from its wartime rival against the exercises that heightened tensions near the western sea border.

The five-day naval exercises, aimed at deterring the Democratic People's Republic of Korea from further aggression after its suspected torpedo attack on a South Korean warship in March, will involve 4,500 troops from the country's army, navy and air force, some 20 vessels and 50 fighter jets, according to Seoul's Joint Chiefs of Staff.

Pyongyang has recently warned of a "powerful physical retaliation" against the drills conducted near the contentious maritime it does not acknowledge, but authorities here dismissed the threat and reiterated their stance that the drills are defensive in nature.

The massive anti-submarine exercises come shortly after South Korea and the United States jointly staged naval and air drills in waters east of the peninsula, also as part of responses to sinking of the warship near the sea border blamed on the DPRK.

Pyongyang has denied any role in the March 26 sinking of the navy corvette Cheonan, which killed 46 South Korean sailors.