Seoul - A North Korean patrol boat Thursday entered the South Korean side of the two nations' disputed western sea border for about one hour, a South Korean official said.

The intrusion took place at 2:47 pm (0547 GMT), the South Korean Yonhap news agency reported, quoting a Joint Chiefs of Staff official. The ship returned into North Korean waters around 3:30 pm after being warned off by South Korea's navy.

Tension between the two Koreas has been on the rise since Pyongyang tested a nuclear device on May 25 and test-fired several missiles in the following days.(dpa)