South Korea and the United States have begun two days of joint naval exercises off the east coast, despite strong objections from North Korea.
Officials said the exercise began when the USS Nimitz strike group left the southern port of Busan early Monday. The U.S. Navy says the carrier's strike group includes guided missile destroyers and a guided missile cruiser.
North Korea called the latest exercise a grave military provocation that would push the peninsula to the brink of nuclear war.
Pyongyang has long denounced joint exercises in the South as a rehearsal for an invasion of the North.