North Korea issued an air raid warning on Thursday, South Korea's Unification Ministry said quoting a radio broadcast monitored in Seoul. A news report said the warning appeared to be part of a defence drill.
The warning was issued at 0032 GMT and carried a message to military units to stand ready, but the action appeared to be a drill under an air raid scenario, Yonhap news agency said.
An official at the Unification Ministry, which handles ties with the North and monitors North Korea's news broadcasts, confirmed air raid warning on Thursday morning.
The official could not confirm whether the warning was part of a drill. The two Koreas remain technically at war under a truce that ended their 1950-53 conflict. Tensions have been high with the rivals exchanging verbal barbs.
North Korea has been conducting large-scale military drills coinciding with annual exercises by the South Korean and U.S. forces running to the end of April. The allies have stressed the drills are strictly defensive in nature.