North Korea has announced a shipping exclusion zone off part of its west coast, a South Korean military official said Tuesday, a move which in the past has sometimes preceded missile test-launches.

The official confirmed to AFP that the North had banned shipping from an area in the Yellow Sea but gave no details. Yonhap news agency said Seoul was watching to see if there were any preparations for a missile launch.

The agency, quoting an unidentified Seoul military official, said the communist state declared a "No sail" zone south of the disputed sea border between the two countries.

The border known as the Northern Limit Line, which the North refuses to recognise, has been a persistent flashpoint. There were deadly naval clashes in the area in 1999 and 2002.

A brief but intense firefight last November left a North Korean patrol boat in flames.

Last month the North warned South Korean ships to avoid the border area, saying its coastal artillery would target it in firing exercises.

Its naval command said at the time its move came in response to "reckless military provocations" from the South.

Naval tensions have remained despite recent efforts by the sanctions-hit North to upgrade or restart joint business projects with the South.