The US and South Korean navies have concluded a major four-day joint naval exercise.
About five South Korean vessels, including two 4,500t destroyers and an anti-submarine aircraft, participated in the drill, according to the Yonhap News Agency.
A US aircraft carrier strike group that included the USS George Washington joined the South Korean ships.
The exercise focused on anti-aircraft defence and anti-submarine drills, such as shooting down hostile aircraft when detected by radar and detecting and destroying enemy submarines using surface warships, submarines and aircraft.
A South Korean Joint Chiefs of Staff senior official said the exercises demonstrated that the allies will respond sternly to any North Korean provocation.