North Korea's Navy Command issued the warning, accusing South Korean navy vessels of repeatedly violating the disputed western sea border in recent days. South Korea denied the allegation.

Hours later, a South Korean navy speedboat fired eight machine-gun rounds at a North Korean fishing boat that sailed 200 yards into waters claimed by the South.

The five-minute encounter in waters 7 miles northwest of this island ended when the Northern trawler turned round, said Kim Sung-ok, a South Korean military spokesman. There was no hostility from the North Korean navy.

Fishermen on Yeonpyeong Island near the disputed sea border and 75 miles west of Seoul fretted that the rising tensions could threaten their livelihoods.

"I'm worried that a naval clash between the two navies would again stop us from going out to catch crabs," said Sung Do-kyong, a 36-year-old fisherman.

The tensions along the inter-Korean sea border come as the United States seeks to rally international pressure on the North to abandon its suspected nuclear weapons programs. North Korea charges that the United States plans to invade.

South Korea's navy ships are "staging a prelude" to a sea skirmish to "provide the US imperialist warhawks, who are blustering that North Korea is next to Iraq, obsessed with war hysteria, with favorable conditions for a war," the North's official news agency KCNA quoted a North Korean Navy Command spokesman as saying Tuesday.

"Now that there is an increasing danger of a nuclear war on the Korean Peninsula, any military clash between the North and the South may lead to a war," he said.

North Korea has never recognized a western sea boundary designated by the United Nations after the end of the 1950-53 Korean War. It claims a boundary farther south.

South Korea says North Korean fishing boats have illegally crossed into its waters almost daily since May 25. It is studying whether the violations were part of a North Korean attempt to escalate tensions and gain leverage in talks with the United States over its nuclear ambitions.

President Bush held separate summits with South Korean President Roh Moo-hyun and Japanese Prime Minister Junichiro Koizumi in May and vowed to take "tougher measures" against North Korea if it escalates tension.

On Monday, Group of Eight world leaders meeting in France accused North Korea of undermining non-proliferation agreements.

The waters off Yeonpyeong have been a site of deadly naval skirmishes in recent years, especially in the June fishing season.

In a gunbattle in June 2002, one South Korean warship sank, killing six sailors. The North said it also suffered casualties, but didn't confirm how many. In a 1999 clash, South Korea said several sailors were wounded, and that up to 30 North Koreans died.

US officials say North Korea claims it has nuclear weapons but is willing to scrap its nuclear programs in return for security guarantees and economic aid.

On Tuesday, North Korea said its military is "fully ready to mercilessly retaliate against the aggressors anytime."

Korea was divided in 1945. The two Koreas share the world's most heavily armed border.

(China Daily June 4, 2003)