North Korea Thursday activated air raid alerts and told its people to take cover in shelters, the South Korean Unification Ministry said after monitoring a broadcast from the North, dpa reported.
It was not clear whether the alert was an actual one or a drill.
The alert could be related to military drills being conducted on the Korean Peninsula. The North's Korean People's Army is conducting drills, and the South Korean and US militaries are also engaged in joint exercises.
Tensions have been high on the peninsula recently as North Korea carried out its third nuclear test in February and issued threats against South Korea and the United States.