SEOUL: North Korea accused South Korea's military Thursday of staging a naval clash this week to raise tensions on the peninsula, and said it would pay dearly for the provocation.

Each side has blamed the other for Tuesday's exchange of fire near the disputed Yellow Sea border, which came just over a week before a scheduled visit to Seoul by US President Barack Obama.

The South has sent one of its newer destroyers equipped with torpedoes and guided missiles closer to the border, military sources told AFP, in addition to two extra patrol boats.

"The South Korean forces will be forced to pay dearly for the grave armed provocation perpetrated by them," the North's official news agency KCNA quoted newspapers as saying.

"The artillery pieces of the KPA (Korean People's Army), convinced of justice and afire with hatred, are now levelled at the provokers," it quoted Rodong Sinmun as saying.

Rodong, the journal of the ruling communist party, said the clash was not accidental "but a deliberate and premeditated provocation" by the South Korean military to try to heighten tension on the peninsula and damage relations.

Seoul says a North Korean patrol boat crossed the border, ignored five warnings to turn back and then opened direct fire at a South Korean boat that had fired a warning shot.

It said South Korean boats returned fire and set the North's boat ablaze.

The North says Seoul's ships opened fire while its craft was north of the border, which was the scene of bloody battles in 1999 and 2002. Chronology: Clashes on Korean peninsula

Its military demands an apology, as do the South's armed forces.

South Korea used 100 times more firepower than the North during the skirmish, riddling the North Korean boat with about 5,000 rounds, a defence official was quoted as saying by Yonhap news agency.

South Korea has put its forces on alert but says it does not want the clash to damage relations. After months of frosty ties, the North has recently put out peace feelers to Seoul and Washington.

Some analysts suspect the North wants to strengthen its bargaining hand in upcoming talks with the United States by raising tensions on the peninsula.

The US special envoy for North Korea, Stephen Bosworth, is expected to visit the North by the end of the year to try to bring it back to six-nation nuclear disarmament talks. Related article: US warns North Korea after naval clash

Secretary of State Hillary Clinton confirmed Wednesday the trip would go ahead despite the naval clash.

The North's Minju Josun government newspaper said it was in fact the South's military which had sought to raise the stakes before Obama's visit and Bosworth's trip.

"By committing this armed provocation, the South's military authorities are seeking to raise animosity against us among their US lords, and to appeal to them not to change their hostile policy against the DPRK (North Korea) and not to engage in DPRK-US talks," it said.

Military sources told Seoul media that one North Korean sailor was killed and three wounded in the exchange of fire, although there was no official confirmation.

No South Koreans were hurt, although one South Korean boat was hit 15 times.

Yonhap quoted an unidentified defence official as saying the North's boat had to be towed on the final stretch of its journey home.

Cross-border tensions have been high for more than a year. The North has also angered the international community with missile test-launches, a walkout from the six-party talks and a second atomic weapons test.

The United Nations tightened sanctions in response.

The North now says it is ready to rejoin the six-nation talks if the US discussions go well.

Washington stresses its bilateral talks are intended only to bring Pyongyang back to the six-party forum, which also includes South Korea, Japan, China and Russia.