Warships from the two sides successfully communicated using a common radio frequency, flags and light signals along a disputed sea border in the Yellow Sea as part of new measures to prevent accidental clashes, navy officials said.

"Navy ships from both sides have been in radio contact from 0000 GMT, sailing along the sea border off the west coast," a South Korean navy spokesman told AFP.

The first exchange of radio messages was made near Yeonpyeong Island when navy ships from both sides sailed close to the sea border. Similar contacts were made at four other locations for two hours.

The unprecedented contact comes a day before the two Koreas hold a series of joint events to mark the signing of a landmark rapprochement agreement at a summit between them in 2000.

A North Korean civilian delegation arrived in South Korea Monday to attend a marathon and other reconciliation events. Pyongyang will also send a government delegation to Seoul this week for a symposium on a railway project linking the peninsula with Europe.

The 2000 summit prompted a thaw between the North and South but ties have been disrupted by naval skirmishes in the rich fishing grounds off the western coast.

Since 1999 dozens of casualties have been reported on both sides. The last clash in June 2002 left six South Korean sailors dead.

Clashes usually occur when fishing boats from one side cross an unmarked maritime border into the other side while chasing fish.

A temporary sea border, called the Northern Limit Line, was drawn in 1953 at the end of the three-year Korean War but North Korea has never recognized it, insisting the sea border should be redrawn.

Monday's contact followed a military deal on June 4 to reduce tensions along the heavily fortified and tense border.

In terms of the accord, the two sides are from midnight Monday to stop propaganda broadcasts along the 248-kilometer (154-mile) land border.

They have also agreed to dismantle all propaganda materials aimed at enticing opposing soldiers to defect.

South Korea has about 100 propaganda billboards along the land border. North Korea has erected 200 huge signs and drawings praising their leader and communism or denouncing the United States.

The border is dotted with loudspeakers, slogans, electronic displays, posters and religious facilities.

The rapprochement comes at a sensitive time, with an international diplomatic drive under way to encourage the Stalinist North to abandon its nuclear ambitions.

North Korea has a 1.1 million-strong force against South Korea's 690,000 troops, who are backed by 37,000 US soldiers.

The United States, however, plans to reduce its troop levels on the peninsula and move US forces away from the border to locations south of Seoul. The plans have triggered security jitters in South Korea.

WAR.WIRE