North Korea says South Korea will pay "an expensive price" for firing at a North Korean patrol boat on Tuesday.

The official Rodong Sinmun newspaper published a commentary Thursday saying the clash in the Yellow Sea was not an accident, but instead was a "premeditated act of aggression" by the South. The commentary said the incident was meant to escalate tensions and dampen a positive atmosphere between the two countries.

This undated handout photo released by the South Korea Navy in Seoul shows high-speed patrol boats armed with canons and machine guns, 10 Nov 2009South Korea's military has been on high alert for possible retaliatory moves after the North Korean boat was set ablaze Tuesday. The South said it fired warning shots after the North Korean patrol crossed its maritime border in the Yellow Sea.

Seoul sent two additional warships to guard the maritime border Wednesday.

U.S. Secretary of State Hillary Clinton said Wednesday the naval clash will not affect Washington's plans to send special envoy Stephen Bosworth to North Korea before the end of the year.

She said the Obama administration will not stop its effort to revive six-country talks on North Korea's nuclear program.

The naval skirmish this week threatened to complicate those negotiations, which involve both Koreas, the U.S., China, Russia and Japan.

Some information for this report was provided by Reuters.