North Korea fired several cruise missiles towards the Yellow Sea in the early hours of Saturday, according to the South Korean military.
Details of the launch were being analyzed by South Korean and U.S. intelligence authorities, 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 on 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 came to a close on 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.
