After Tuesday's brief naval clash in the Yellow Sea South Korean troops have been placed on high alert for possible retaliation from the North.
The clash was the first such engagement in seven years, reportedly leading to the death of at least one North Korean sailor and stoking fresh tensions between the rival Koreas.
Kim Tae-young, South Korea's defence minister, said he believed the North may take retaliatory action and said the president had ordered the military onto a heightened state of alert.
South Korea 's joint chiefs of staff said in a statement that a North Korean patrol boat crossed the disputed border line in the Yellow Sea before noon on Tuesday, drawing warning shots from a South Korean navy vessel, Aljazeera.net reports.
It was also reported, this week's naval clash between two Koreas will not affect the decision to send a U.S. special envoy to North Korea, U.S. Secretary of State Hillary Clinton said on Wednesday.
"This does not in any way affect the decision to send ambassador Bosworth. We think that this is an important step that stands on its own," Clinton told a news conference on the sidelines of an APEC meeting in Singapore.
The rival Koreas exchanged gunfire, damaging vessels on both sides and raising tension just before U.S. President Obama travels to Asia, Reuters reports.
Yoon Deok-min, a professor at South Korea's state-run Institute of Foreign Affairs and National Security, said the North has a track record of making provocations ahead of important negotiations.
"It is aimed at extracting concessions from the U.S. by making it seem as if hawks are pitted against doves in Pyongyang ahead of negotiations," he said.
Another analyst, Ralph Cossa, president of the Pacific Forum CSIS think tank in Honolulu, Hawaii, said North Korea could have staged the clash as a "dress rehearsal" for further provocations
"I think it's still possible to see more naval activities" next week as the North could try to draw attention away from Seoul during Obama's Nov. 18-19 stop in South Korea, The Associated Press reports.
Su-35 and Su-30 fighters were carrying out a scheduled training flight, when the incident occurred