South Korea warned it was ready to deter any retaliation by North Korea following the two countries' first naval clash in seven years, reportedly deploying two warships to the disputed sea border Wednesday.

The skirmish will not deter Washington from sending an envoy to North Korea, U.S. Secretary of State Hillary Rodham Clinton said, vowing to continue efforts to resolve long-standing disputes over Pyongyang's nuclear weapons program.

Tuesday's exchange of fire occurred hours before U.S. officials said President Barack Obama had decided to accept a North Korean invitation to send the envoy to Pyongyang for the first direct talks during his administration. The incident sparked speculation that the North was trying to foment tensions to gain a negotiating advantage.

The naval clash "does not in any way affect our decision" to send envoy Stephen Bosworth to Pyongyang, U.S. Secretary of State Hillary Rodham Clinton said in Singapore on Wednesday. "We think it is an important step that stands on its own."

Bosworth's trip is aimed at persuading communist North Korea to return to six-nation nuclear disarmament negotiations that it walked away from earlier this year.

Both sides blamed the other for Tuesday's two-minute clash in a crab-fishing area off the countries' west coast, where both sides regularly accuse the other of violating the disputed border. North Korea's military demanded that the South apologize.

The South deployed two more navy ships to deal with possible North Korean moves along the disputed western sea border, South Korea's Yonhap news agency reported Wednesday, citing an unidentified military source.

The Defense Ministry and Joint Chiefs of Staff said they could not confirm the report.

South Korea's National Intelligence Service said Tuesday's incident could not have been an accidental intrusion by North Korea, according to a ruling party lawmaker who is a member of parliament's intelligence committee. He did not elaborate and asked not to be identified, citing the issue's sensitivity.

Phone calls to the intelligence service seeking comment went unanswered late Wednesday.

South Korean Prime Minister Chung Un-chan had said Tuesday that the North Koreans may have been clamping down on Chinese fishing vessels in the area, and probably did not intend to violate the border.

South Korean officials said the North Korean ship was on fire and heavily damaged when it retreated. The South Korean ship was lightly damaged and there were no South Korean casualties, according to the Joint Chiefs of Staff.

One North Korean officer was killed and three other sailors were wounded in the clash, a senior South Korean military officer told The Associated Press late Wednesday, confirming earlier South Korean media reports. He spoke on condition of anonymity because the matter involved intelligence.

Defense Minister Kim Tae-young told the National Assembly on Tuesday that he believed the North may take retaliatory actions, saying President Lee Myung-bak "also has such concerns."

South Korea has detected no unusual North Korean troop movements but placed its 680,000-strong military _ one of the world's largest _ on heightened alert, the Joint Chiefs of Staff said.

Relations between the two Koreas became badly frayed after Lee took office last year with a tough line on the North, which responded by cutting off ties and threatening war.

The situation further deteriorated following nuclear and missile tests by the North this year. Recently, however, North Korea has made a series of conciliatory gestures, such as releasing South Korean and American detainees and agreeing to resume joint projects with Seoul. Continued...