North Korea fired several cruise missiles toward the Yellow Sea early Saturday, the South Korean military said.
South Korean and U.S. intelligence authorities were analyzing details of the launch, South Korea's Joint Chiefs of Staff said in a statement.
It was the latest in a series of missile tests and military exercises conducted by the North in recent weeks, including a failed spy satellite launch late last month.
Seoul announced sanctions Friday on five North Korean individuals and one company in response to Pyongyang's launch of what it said was a space rocket last month.
On Thursday, state media KCNA reported that Pyongyang had conducted a simulated "scorched earth" nuclear strike on targets across South Korea, drawing criticism from Seoul.
The joint annual summertime exercises between South Korea and the U.S. known as the Ulchi Freedom Shield ended Thursday after an 11-day run featuring air drills with B-1B bombers.
North Korea protested the deployment of the U.S. strategic bombers by firing two ballistic missiles just hours later in retaliation.
Pyongyang has long denounced the drills as a rehearsal for war.
