Jet fighters on US aircraft carrier USS Ronald Reagan. (Photo: VNA)

The drills came as Seoul and Washington crank up security cooperation amid continued speculation that Pyongyang could engage in provocative acts, like a nuclear test or submarine-launched ballistic missile (SLBM) launch.

The four-day exercise got under way with the presence of the nuclear-powered USS Ronald Reagan carrier to demonstrate the “strong will” of the South Korea-US alliance and hone their military capabilities for combined operations, navy officials here said.

The exercise involves various drills on anti-ship and anti-submarine warfare operations, tactical maneuvers and other maritime combat operations.