North Korea fired at least one short-range ballistic missile on Thursday, South Korea's military said. In this January photo, people watch a news report of a North Korean missile launch at Seoul Station. File Photo by Jeon Heon-Kyun/EPA

North Korea fired at least one short-range ballistic missile toward the East Sea on Thursday, South Korea's military said.

The Joint Chiefs of Staff (JCS) said the missile was launched from the eastern coastal Wonsan area in the North at around 5 p.m.

The number of missiles launched was not immediately known.

"While strengthening monitoring and surveillance against potential additional launches, our military is maintaining a full readiness posture and closely sharing relevant information with the United States and Japan," the JCS said.