North Korea issued an air raid warning and put its military on alert Thursday, South Korea's Unification Ministry said, in what appeared to be a drill at a time of heightened tensions.
The public air raid alert was issued through state radio, a ministry spokeswoman told AFP.
"We assume it' s an air defence drill," another government official said.
Military tensions on the Korean peninsula are at their highest level for years, with North Korea -- angered by UN sanctions imposed after its nuclear test last month -- threatening a second Korean War backed by nuclear weapons.
Pyongyang has also denounced ongoing joint South Korea-US military manoeuvres, involving nuclear-capable B-52 bombers, calling them a provocative rehearsal for invasion.
A Defence Ministry spokesman noted that North Korea had been carrying out its own military exercises and that the air raid warning was most likely part of that exercise.