****(Note From Snake: I figured Russia would get involved!)****
South Korean President Lee Myung-bak has described as an "inhumane crime" the North's deadly shelling of a Southern island last Tuesday.
Mr Lee said he felt deep responsibility for failing to protect residents of Yeonpyeong island, where four South Koreans were killed.
Pyongyang says it was provoked by Seoul's military drill near Yeonpyeong.
Tension remains high in the area, where the US and South Korea are currently holding joint military exercises.
The North has described the four-day drill in the Yellow Sea, near the disputed border between the two Koreas, as a provocation.
Speaking on Monday, Mr Lee pledged that Pyongyang "will pay the price in the event of further provocations".
"Attacking civilians militarily is an inhumane crime that is strictly forbidden in a time of war. I cannot help expressing anger at the North Korean regime's brutality," the president said in an address to the nation - his first since Tuesday's attack.
Mr Lee did not elaborate on how Seoul might respond on any possible provocation by Pyongyang in the future.
The president used very firm language in his speech, the BBC's Chris Hogg in Seoul reports.
Mr Lee's government has been criticised by opposition lawmakers and by some from his own party who say the military response to the response to the shelling was too soft and too slow, our correspondent adds.
The president's comments come a day after China called for an emergency meeting of key nations to try to defuse the tension.
Beijing proposed that members of the six nations that have been taking part in talks on North Korean nuclear disarmament should meet in December.
The two Koreas, the US, China, Japan and Russia are involved in the talks.