North Korea threatened Wednesday to block cross-border traffic and blow up any South Korean loudspeakers blasting propaganda northward after a six-year hiatus, 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 homing 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 North Korea — ranging from 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, Pyongyang 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 factory 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.
The statement 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.
"The South Korean puppet warlike forces would be well advised to act with discretion, bearing deep in mind that such measures of the Korean People's Army will not end in an empty talk," said the statement, carried by the official Korean Central News Agency.
Despite the rhetoric, North Korea still allowed South Koreans workers to cross the border to enter the Kaesong complex Wednesday, according to the Unification Ministry.
The North's statement Tuesday did not refer to about 800 South Korean company managers and workers at Kaesong. Seoul also excluded Kaesong — the last remaining major joint reconciliation project that provides badly needed hard currency for Kim Jong Il's regime — from its retaliatory measures.
South Korea accused North Korea of taking "menacing" measures and will "deal with these North Korean threats unwaveringly and sternly," Unification Ministry spokesman Chun Hae-sung said Wednesday.
South Korea's military said Wednesday there were no signs of unusual activity by North Korean troops.
A Seoul-based monitoring agency reported Tuesday that North Korean leader Kim ordered the country's 1.2 million-member military to get ready for combat. South Korean officials could not immediately confirm the report. North Korea often issues fiery rhetoric and regularly vows to wage war against South Korea and the United States.
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 have technically remained 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.
The U.S. Air Force said in a statement last week that it plans to deploy 12 F-22 fighters each to Guam and Japan later this month for about four months. The statement said the deployment illustrates "the flexibility U.S. forces have to meet their ongoing commitments and security obligations throughout the Pacific region." The release made no mention of the ship sinking or tensions on the Korean peninsula.
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.
Relations are at their lowest point since a decade ago, when South Korea began reaching out to the North with unconditional aid as part of reconciliation efforts. Lee has taken a harder line since taking office in 2008, and the South has suspended aid.
Associated Press writers Sangwon Yoon and Matthew Lee and AP photographer Young-joon Ahn contributed to this report.
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