U.S. and South Korean forces held a landing drill Monday near the port city of Pohang, as part of the annual Foal Eagle military exercise.
South Korean military officials said the drill mobilized about 7,600 navy and marine personnel and 30 naval vessels, as well as several landing crafts.
Earlier this month, North Korea fired two short-range missiles off its east coast, hours before the joint military exercises began.
North Korea regularly protests the joint drills, which it calls a rehearsal for invasion.
Foal Eagle runs through April 24.