SEOUL, South Korea - North Korea threatened Wednesday to block cross-border traffic and blow up any South Korean loudspeakers blasting propaganda northward as tensions soared over the sinking of a South Korean warship.
The dramatic deterioration in relations came as U.S. Secretary of State Hillary Rodham Clinton visited Seoul at the end of a three-nation Asian tour that was dominated by the March 26 sinking blamed on a North Korean torpedo attack.
"This was an unacceptable provocation by North Korea, and the international community has a responsibility and a duty to respond," Clinton told reporters after talks with South Korean leaders.
A team of international investigators concluded last week that a torpedo from a North Korean submarine tore apart the 1,200-ton Cheonan off the west coast, killing 46 South Korean sailors.
South Korea began taking punitive steps Tuesday against the North including slashing trade, resuming propaganda warfare and barring the North's cargo ships. Those were seen as among the strongest it could implement short of military action.
The U.S. has said evidence of the North's culpability is overwhelming and has backed the South's measures, but key North Korea ally China has said it is still weighing evidence about the sinking and has done little but urge calm on all sides.
"I believe that the Chinese understand the seriousness of this issue and are willing to listen to the concerns expressed by both South Korea and the United States," said Clinton, who visited China before coming to Seoul. "We expect to be working with China as we move forward in fashioning a response."
The North flatly denies it caused the sinking and has warned that retaliation would lead to war. On Tuesday, North Korea announced it was cutting relations with South Korea, starting "all-out counterattacks" against the South's psychological warfare operations and barring South Korean ships and airliners from passing through its territory.
On Wednesday, the North cut off some cross-border communication links and expelled eight South Korean government officials from a joint industrial park in the North Korean border city of Kaesong, South Korea's Unification Ministry said.
The North's military also issued a statement warning it would "totally ban" the passage of South Korean personnel and vehicles to an inter-Korean zone in the western coastal area, apparently referring to Kaesong, if South Korea does not stop its psychological warfare. It did not mention another border crossing on the eastern side of the peninsula, which remained open.
It said it would shoot at and "blow up" any loudspeakers South Korea installs at the border. Seoul dismantled such devices six years ago amid warming ties, but resumed radio broadcasts Monday into the North and said loudspeakers would be reinstalled within weeks.
In Pyongyang, North Korea's capital, army generals vowed to retaliate against South Korea.
"We will never tolerate the slightest provocations of our enemies, and will answer to that with all-out war," Maj. Gen. Pak Chan Su, a Korean War veteran, said, according to footage from APTN in Pyongyang. "This is the firm standpoint of our People's Army."
Ordinary citizens also criticized the South.
"The South Korean puppet authorities are raving like a mad man, linking the sinking of the Cheonan with us but the truth will be revealed," said Ri Gyong Dok, a Pyongyang resident. "We value inter-Korean relations, but the puppet authorities challenging and scheming for a war -- this cannot be tolerated."
Despite the rhetoric, North Korea still allowed South Korean workers to cross the border to enter the Kaesong complex Wednesday, according to the Unification Ministry.
Kaesong is the last remaining major inter-Korean reconciliation project. It provides badly needed hard currency for Kim Jong Il's government and is valued in the South as a source of engagement with the isolated communist country. Both sides have refrained from calling for its closure in their recent statements.
South Korean Unification Ministry spokesman Chun Hae-sung accused North Korea of taking "menacing" measures and said the South would "deal with these North Korean threats unwaveringly and sternly."
South Korea's military said Wednesday there were no signs of unusual activity by North Korean troops.
South Korea wants to bring North Korea before the U.N. Security Council over the sinking, and has U.S. support.
The North and South technically remain at war since the 1950-53 Korean War ended with an armistice rather than a peace treaty.
The U.S. and South Korea are planning two major military exercises off the Korean peninsula in a display of force intended to deter future aggression by North Korea, the White House said. The U.S. has 28,500 troops in South Korea.
Also Wednesday, more than 3,000 South Korean veterans of the Korean and Vietnam wars and their family members rallied in Seoul, burning an effigy of Kim Jong Il and chanting anti-North Korea slogans.
