S Korea boats fire border warning

The two sides clashed seriously in 2002

South Korean patrol boats have fired warning shots after North Korean navy vessels crossed their disputed maritime border, the South said.

A South Korean statement said three boats crossed the so-called Northern Limit Line in two incidents on Monday.

"Three North Korean patrol boats crossed... and retreated back north after warning messages and shots from our navy," the statement said.

Such incidents are not unusual, but still serve to heighten tensions.

Naval clashes in 1999 and 2002 left several people dead, and led to both sides agreeing new measures to reduce tensions.

TROUBLESOME BORDER Known as Northern Limit Line Position declared by UN in 1953 Not recognised by North Regularly breached by North's fishermen

These measures included a telephone hotline and sharing radio frequencies.

The South Korean statement said 80 boats were near the naval border on Monday.

The incident may have been caused by a large fleet of Chinese fishing vessels that were in the area.

A South Korean official told AFP that the North Korean boats had said they were checking on the Chinese fishermen.