South Korea and the United States staged combined anti-submarine drills, involving a US nuclear-powered submarine, in waters south of the Korean Peninsula on Saturday, Seoul's Navy said, amid joint efforts to reinforce readiness against North Korean military threats.

The exercise took place in waters south of the southern island of Jeju, mobilizing the South's ROKS Yulgok Yi I Aegis-equipped destroyer, the ROKS Yi Sun-sin submarine and the US' USS Annapolis submarine, according to the armed service.

The drills focused on training response procedures against a simulated North Korean submarine, such as searching for, tracking and identifying the target, the Navy said.

"This exercise was prepared to strengthen the South Korean and US navies' response capabilities and enhance interoperability in preparation against North Korean submarine infiltrations amid growing threats from North Korea's missile provocations," the armed service said.

North Korea fired two short-range ballistic missiles into the East Sea on Monday, after the US' Los Angeles-class submarine's arrival at a naval base on Jeju earlier in the day. (Yonhap)