The North Korean boat crossed a tense inter-Korean sea border off Baekryeong Island into southern waters for nine minutes before being chased back, according to the South's Joint Chiefs of Staff (JCS) office.

"The boat sailed back into North Korean waters when our navy sent two ships to stop the incursion across the Northern Limit Line (NLL)," a JCS spokesman told AFP.

The incursion came as the two Koreas opened high-level talks in Seoul on their rapprochment amid a prolonged stand-off over the communist country's nuclear weapons drive.

The NLL has served as a de-facto maritime border between South and North Korea since the 1950-53 war, but the North has never recognized it.

Disputes over the NLL and its surrounding rich fishing grounds have led to two naval battles in recent years.

A naval skirmish on June 29, 2002, left six South Korean soldiers dead. In June 1999, a similar skirmish killed dozens of North Korean sailors.

South Korean warships fired warning shots last month on North Korean fishing boats which violated the maritime border.

WAR.WIRE