Shots fired

South Korea has fired shots at a North Korean ship.

North Korea criticized South Korea on Tuesday for firing warning shots at one of its navy patrol boats and warned of "grave consequences."

South Korea's military said it fired the shots Monday after a North Korean navy patrol boat entered waters controlled by the South. The Northern boat retreated without resistance.

A North Korean military source described the encounter as "a barrage of gun shells" fired at a communist navy boat on routine patrol, according to KCNA, the North's official news agency.

"The South Korean military authorities should refrain from acting rashly, pondering over the grave consequences to be entailed by such reckless military provocation," KCNA quoted the military source as saying.

North Korea often issues such threatening remarks to its southern neighbor.

The maritime border between the two Koreas is not clearly marked, and North Korean fishing boats often enter its neighbor's waters. South Korean navy ships occasionally respond with warning shots.