Despite previous warnings of retaliation from North Korea, the South Korean military continued to defy the North on Wednesday by launching a three-day naval drill in the Sea of Japan and scheduling an exercise by the army and air force about 30 miles from the North-South demilitarized zone. The naval exercise, scheduled to last three days, was expected to take place about 60 miles south of the maritime border in waters off the east coast of the Korean Peninsula. An official at the Defense Ministry said there would be no shelling during the drill. A one-day artillery exercise also was planned for Thursday, the defense official said, at a firing range near Pocheon, about 25 miles northeast of Seoul. He denied news reports in Seoul that called it the largest live-fire drill ever to be held near the demilitarized zone, or DMZ. Instead, the official characterized the drill as ordinary.