BEIJING - A defiant North Korea said Tuesday that it would sever all ties with South Korea, cut off communications, and expel workers from a jointly run industrial park in a bellicose response to the South's efforts to seek redress for the sinking of one of its ships.

Although South Korea has said it would not retaliate with force, instead seeking sanctions through the U.N. Security Council, Pyongyang earlier in the day accused Seoul of making a "deliberate provocation aimed to spark off another military conflict."

In Beijing, Secretary of State Hillary Rodham Clinton said the United States stood firmly behind South Korea and urged China to join in condemning North Korea's behavior, as Beijing did last year when the North tested a nuclear weapon.

"We expect to be working together with China in responding to North Korea's provocative action, and promoting stability in the region," Clinton said at the conclusion of two days of talks with Chinese officials that were supposed to concentrate on economics, but ended up being overshadowed by the Korean crisis.

Clinton flies Wednesday to Seoul for meetings with Japanese and South Korean officials. Chinese Premier Wen Jiabao is also headed to Seoul to meet Friday with South Korean President Lee Myung Bak.

P. J. Crowley, the chief State Department spokesman, said North Korea's decision to sever ties with the South was "odd," given the potential benefits to the impoverished state of stronger ties to their wealthier neighbor.

The South Korean naval vessel Cheonan was on patrol in the Yellow Sea on March 26 when an explosion ripped apart the hull, killing 46 crew members. Investigators last week declared what was already widely believed in South Korea: that the sinking was the result of an attack by a North Korean torpedo.

North Korea shows no signs of flinching in what is increasingly a battle of nerves with South Korea.

Pyongyang issued a flurry of threats during the day. It accused South Korea of dispatching "dozens" of warships across the maritime border and said that it would "put into force practical military measures to defend its waters."

North Korea said it had given permission for its soldiers to shoot at South Korean loudspeakers - a response to an announcement Monday that Seoul would resume broadcasting propaganda across the demilitarized zone that divides the peninsula.

The strongest measure, announced late in the day, was the severing of all relations and communications with South Korea. As a practical matter, that would mean closing an industrial park in Kaesong, just north of the DMZ, which was once the showcase for cooperation between the Koreas. More than half a century after the 1950-53 Korean War, there is still no telephone or postal service between the countries.

The threats looked like a tried-and-true North Korean maneuver - escalating the tensions to remind South Korea how vulnerable its economy is to any hint of renewed conflict. The Korean won dropped to its lowest level in 10 months, and stocks throughout Asia sank in part on fears of war.

"The North Koreans have an advantage here in that the South Koreans have a greater fear of war," said Scott Snyder, an Asia Foundation expert who cowrote a book about North Korea's negotiating behavior.

Although the South Korean public is outraged about the sinking of the ship, it has no appetite for a military response to the North.

"This has been characterized as South Korea's 9/11," Snyder said, "but people know that any military response would just bring them greater pain."

On the other hand, North Korean leader Kim Jong Il might be able to exploit rising tensions with South Korea to distract his nation's citizens from the abysmal state of their economy. His popularity has suffered because of a botched currency reform late last year. The ailing 68-year-old leader is also in the process of trying to install his youngest son, who is in his 20s, as his successor.

"Dictatorships undergoing internal political turmoil generally manifest belligerent external behavior," said the Washington-based Center for Strategic and International Studies in a report released Tuesday.