SEOUL (REUTERS) - South Korea and the UN Command, which oversees the Korean War armistice, said on Friday (June 10) they had begun a joint operation to keep Chinese fishing vessels from operating illegally off the west coast.

The move comes after South Korean fishermen, frustrated with incursions by Chinese fishing boats in defiance of coast guard warnings, used rope to impound two Chinese trawlers this month and handed them over to authorities.

South Korea's navy and coast guard joined with the UN Command to patrol the approximately 60km stretch of waters in the Han River estuary that runs between the coasts of the rival Koreas, a Defence Ministry official told Reuters.

"Our navy, coast guard and UN Command set up a military police to enter into an operation to expel Chinese fishing vessels," said the official.

North Korea had been notified of the team's operation as a safety precaution, an official at the Joint Chiefs of Staff said separately.

North and South Korea are technically still at war because their 1950-53 conflict ended in the armistice, not a peace treaty.

There were more than 10 Chinese boats fishing in the estuary on Friday but they fled to areas near North Korea's shore after the South Korean-UN operation began, the Joint Chiefs of Staff official said.

There was no immediate comment from the Chinese Foreign Ministry when contacted by phone.

The waters are near the Northern Limit Line, the maritime border disputed by the North which has been the scene of deadly naval clashes between the rival Koreas and violent confrontation between South Korea's coast guard and Chinese fishing vessels.

South Korea has repeated its complaint to China about illegal fishing by Chinese trawlers since the capture of the two vessels. South Korean Foreign Ministry spokesman Cho Joon Hyuk urged Beijing on Thursday to help come up with a permanent solution.