A South Korean man at a railway station in Seoul watches footage Tuesday of South Korean sailors in a 2002 clash with the North Korean navy. The video was broadcast after the latest naval clash between the countries. (Ahn Young-joon/Associated Press)

U.S. Secretary of State Hillary Rodham Clinton is urging calm in the wake of a naval skirmish between North and South Korea this week, and says diplomatic efforts to resolve the nuclear standoff with the North will continue.

As South Korea placed its military on heightened alert and warned it was ready to deter any retaliation by the North, Clinton said Tuesday's skirmish would not affect U.S. President Barack Obama's decision to send a special envoy to Pyongyang "in the near future."

Speaking Wednesday on the sidelines of the Asia-Pacific Economic Co-operation forum in Singapore, Clinton said the envoy, Stephen Bosworth, would go to North Korea as planned to try to persuade the communist nation to return to stalled six-country nuclear disarmament talks.

"We are certainly counseling calm and caution when it comes to any kind of dispute, ... but at the same time we are moving ahead with our planned visit for Ambassador Bosworth," she said. "We think that it is an important step that stands on its own."

The talks will be the first between the United States and North Korea since Obama took office in January. The two countries, which fought on opposite sides in the 1950-53 Korean War, do not have diplomatic relations.

"We have made the purpose and parameters of this visit clear to the North Koreans," Clinton said. "This is not a negotiation. It is an effort to pave the way toward North Korea's return to the six-party process."

North Korea quit the negotiations earlier this year in anger over international criticism of its nuclear and missile programs, but has reached out to Washington in recent months with calls for bilateral talks.

The Obama administration has said it is open to holding direct talks if they lead to a resumption of the disarmament negotiations.

Skirmish in crab grounds

The two-minute exchange of gunfire Tuesday between North and South Korean warships at the countries' disputed maritime border reportedly left one North Korean sailor dead and three wounded. The South Korean military reported no casualties and said the North Korean ship was on fire and heavily damaged when it retreated.

Both sides blamed the other for the clash in a rich crab-fishing area off the countries' west coast, where both sides regularly accuse the other of violating the disputed border. Deadly skirmishes in the area also took place in 1999 and 2002.

Tuesday's hostilities occurred just hours before confirmation from Washington that Obama, who will be visiting Japan and South Korea in the coming days, had decided to accept North Korea's invitation to bilateral talks. It sparked speculation that the North is trying to foment tensions to gain a negotiating advantage.

In Seoul, Defence Minister Kim Tae-young told the National Assembly on Tuesday that he believed the North may take retaliatory action, saying South Korean President Lee Myung-bak "also has such concerns."

On Wednesday, though, South Korea's presidential office said it didn't want ties with North Korea to deteriorate as a result of the skirmish. Still, several hundred protesters gathered in Seoul to vent their anger at North Korea, burning flags and pictures of North Korean leader Kim Jong-il.

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.