South Korea's military remains on a heightened state of alert after Saturday's lethal clash off the west cost of the peninsula. Four South Korean sailors were killed, 19 wounded and one is missing. South Korea's president did not cancel his planned visit to Japan but remains in close contact with defense officials.
South Korean President Kim Dae-jung went to Japan Sunday to attend the World Cup final that Japan and South Korea are jointly hosting. He said his government will take the necessary actions to deal with Saturday's deadly shoot-out with North Korean ships.
South Korea maintains two North Korean patrol ships intruded across a disputed Yellow Sea border and fired on its boats. Seoul is demanding an apology for what it calls an "intolerable provocation" from its communist neighbor. South Korea's Yonhap news agency said Seoul will pursue "strong military steps" but it did not give details.
But through it state-run media, North Korea blames the South for starting the incident and says its forces were acting in self-defense.
Washington has condemned North Korea's attack on its South Korean ally and warns that the incident may delay the visit of a high-level U.S. delegation to Pyongyang planned for next month.
China, with strong ties to both the North and South, is urging the two sides to maintain stability.
The two Koreas have been divided since the 1950 to 1953 war and coexist in a state of armed truce. Their land border remains sealed and heavily guarded, but the sea border is less clearly marked.
This is the first serious sea clash between the Koreas since 1999 and is a serious setback for South Korea's reconciliation policy with Pyongyang. In the 1999 incident, the worst since the end of the Korean War, one North Korean naval boat sank and three of its warships were severely damaged. At least 30 North Korean soldiers are believed to have died and 70 others were injured. Seven South Korean naval personnel sustained minor injuries.
Saturday's clash, which took place in a rich fishing ground, came after a series of maritime border incursions by North Korean warships and fishing boats into South Korean territorial waters. Two North Korean patrol boats briefly crossed the border Friday in the 10th such violation this year. South Korea accuses North Korea of making 12 brief border violations last year.