Clash in Korean coastal waters

The South Korean Defence Ministry says its Navy has fired warning shots at three North Korean fishing boats after they entered the South's territorial waters along the western sea border.

There are no immediate reports of casualties. The incident occurred near the island of Yongpyong, west of the Korean Peninsula.

It was the sixth encounter along North and South Korea's disputed western sea border in the past seven days.

South Korea says it is studying whether the repeated North Korean violations are intentional.

The latest tensions come amid a continued stand-off over the North's nuclear programme.

Border not recognised

On Thursday, Pyongyang warned Seoul of "irrevocable serious consequences" after accusing South Korean warships of repeatedly violating its territorial waters off the western coast.

North Korea has never recognised the Northern Limit Line (NLL), which serves as a de-facto maritime border between South and North since the 1950-53 war.

Correspondents say Northern fishing boats occasionally cross the NLL during crab catching season.

In recent years, the navies of the two Koreas have confronted each other in the area.

In 1999, up to 30 North Koreans were believed to have been killed in a skirmish. A similar incident last year, left six Southern soldiers dead and a patrol boat sunk.