The drills began 6 a.m. local time (4 p.m. ET) in the Yellow Sea, west of the Korean peninsula town of Taean, south of the site of Tuesday’s attack, according to Korean military officials quoted by Yonhap and Reuters news agencies.

However, officials told NBC News that the maneuvers would not start until midafternoon as the nuclear-powered aircraft carrier USS George Washington had just arrived in the area to join the exercise. They added that no live-fire exercises are planned during the three-day war games.