SKorea troops on high alert after navy battle

The clash Tuesday along the disputed western sea border was the first such engagement in seven years, sending tensions soaring about a week before Obama travels to Seoul as part of his Asian tour.

The exchange of fire also occurred just hours before the State Department announced a senior U.S. diplomat will travel to North Korea before year's end to try to entice North Korea back into international negotiations on nuclear disarmament. The dispatch of envoy Stephen Bosworth would mark the first direct talks between Washington and Pyongyang since Obama took office in January.

South Korean officials said the North Korean ship was on fire and heavily damaged following a two-minute skirmish off the west coast -- the scene of two bloody naval battles in 1999 and 2002. The South Korean ship was only lightly damaged and there were no South Korean causalities, according to the Joint Chiefs of Staff.

South Korea's mass-circulation Chosun Ilbo newspaper and other media reported that one North Korean officer was believed killed and three other sailors wounded. President Lee Myung-bak ordered his Defense Minister Kim Tae-young to strengthen military readiness.

Late Tuesday, Kim said in parliament that he believed the North may take retaliatory action. "The president also has such concerns," Kim said.

South Korea's 680,000-strong military was on heightened alert but detected no unusual North Korean troop movements, an officer at the Joint Chiefs of Staff said.

Asked if U.S. troops in South Korea had raised their alert level, David Oten, a spokesman for the U.S. military in Seoul, said it does not comment on operational or security issues. The U.S. stations about 28,500 troops in South Korea to deter possible North Korean aggression.

The officer, speaking on condition of anonymity citing department policy, said the heightened posture meant having troops stay vigilant but that there were no additional deployments in border areas. South Korean ships did routine patrols along the sea border Wednesday, he said.

Presidential security adviser Kim Sung-hwan was quoted as saying by Yonhap news agency that signs of a North Korean retaliation have not been detected. Kim, however, said North Korea may take time before retaliating.

Yonhap also quoted an unidentified government official as saying that North Korea had also put its troops on high alert.

The Koreas blamed each other Tuesday for causing the skirmish in the rich crab-fishing area, where both sides regularly accuse the other of border violations.

A North Korean patrol boat crossed the disputed sea border before noon on Tuesday, drawing warning shots from a South Korean navy vessel, South Korea's Joint Chiefs of Staff said in a statement. It said the North Korean boat then opened fire and the South's ship returned fire before the North's vessel sailed back toward its waters.

The ships were about two miles (3.2 kilometers) apart during the clash, South Korean Rear Adm. Lee Ki-sik told reporters.

North Korea's military said its ship was attacked by South Korean vessels as it was returning from checking on "an unidentified object that intruded" into its waters.

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

Some South Korean analysts, however, said North Korea was sending a clear message ahead of Obama's two-day visit starting next Wednesday.

"It was an intentional provocation by North Korea to draw attention ahead of Obama's trip," said Shin Yul, a political scientist at Seoul's Myongji University.

Traveling with Obama on Air Force One, White House spokesman Robert Gibbs said the administration was aware of the clash and urged North Korea not to escalate tensions.

The two Koreas are still technically at war and the U.S., which fought as part of U.N. forces on South Korea's side, has never had diplomatic relations with North Korea.

Washington has consistently said that Pyongyang must abandon its nuclear arsenal for any peace treaty to be concluded. North Korea has conducted two underground nuclear tests since 2006 and is believed to have enough weaponized plutonium for half a dozen atomic weapons.

The U.S. will send Bosworth to North Korea in part of its efforts to get the North to return stalled six-nation nuclear talks involving the two Koreas, the U.S., China, Russia and China.

Some analysts said the clash could have been accidental.

"This is not the first naval incident, and it is a border area where both sides have different claims," Charles Morrison, president of the Honolulu-based East-West Center, said in Singapore. "So it's possible it's an error."

South Korea's military said North Korean ships have violated the sea border 22 times this year. North Korea last month accused South Korean warships of broaching its territory and warned of a clash.

No South Koreans were killed in 1999, but six South Korean sailors died in 2002, according to the South Korean navy. It said exact North Korean causalities remain unclear.

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Associated Press writers Kelly Olsen and Kwang-tae Kim in Seoul, National Security Writer Robert Burns in Washington, Ben Feller on Air Force One and Alex Kennedy in Singapore contributed to this report.