N. Korea fires unspecified missile

North Korea fired an unspecified missile from a submarine over the weekend, Seoul's military said Monday, in apparent protest over a regular South Korea-U.S. combined military exercise to begin this week.

The Joint Chiefs of Staff (JCS) said that it detected the missile launched from the North's eastern coastal city of Sinpo on Sunday morning. It did not immediately provide other details.

"While strengthening its monitoring and vigilance, our military is maintaining a full readiness posture in close cooperation with the United States," the JCS said in a text message sent to reporters.