PAJU, South Korea (AP) - North Korea on Wednesday barred South Korean workers from entering a jointly run factory park just over the heavily armed border in the North, officials in Seoul said, a day after Pyongyang announced it would restart its long-shuttered plutonium reactor and increase production of nuclear weapons material.
The move to block South Koreans from going to their jobs at the Kaesong industrial complex, the last remaining symbol of detente between the rivals, comes amid increasing hostility from Pyongyang, which has threatened to stage nuclear and missile strikes on Seoul and Washington and has said that the armistice ending the 1950s Korean War is void.
Seoul's Unification Ministry spokesman Kim Hyung-suk said Pyongyang was allowing South Koreans to return home from Kaesong. Three workers returned Wednesday morning; dozens more were scheduled to return later. But Kim said about 480 South Koreans who had planned to travel to the park Wednesday were being refused entry.
North Korean authorities cited recent political circumstances on the Korean Peninsula when they delivered their decision to block South Korean workers from entering Kaesong, Kim said without elaborating.
It's the latest sign of deepening tensions on the Korean Peninsula. North Korea said Tuesday that it will quickly begin "readjusting and restarting" the facilities at its main Nyongbyon nuclear complex, including the plutonium reactor and a uranium enrichment plant. Both could produce fuel for nuclear weapons. Analysts saw the statement as Pyongyang's latest attempt to extract U.S. concessions by raising fears of war. Experts estimate reactivating the reactor could take anywhere from three months to a year.
The rising tide of threats in recent weeks are seen as efforts by the North to force new policies in Seoul, diplomatic talks with Washington and to increase domestic loyalty to young North Korean leader Kim Jong Un by portraying him as a powerful military commander.
North Korea is angry about ongoing South Korea-U.S. military drills and new U.N. sanctions over its Feb. 12 nuclear test, its third. The Korean Peninsula technically remains in a state of war because a truce, not a peace treaty, ended the Korean War. The United States stations 28,500 troops in South Korea as a deterrent to North Korea.
The North's plutonium reactor began operations in 1986 but was shut down as part of international nuclear disarmament talks in 2007 that have since stalled. Tuesday's nuclear announcement underscores worries about North Korea's timetable for building a nuclear-tipped missile that can reach the United States, although it is still believed to be years away from developing that technology.
The North's rising rhetoric has been met by a display of U.S. military strength, including flights of nuclear-capable bombers and stealth jets at the annual South Korean-U.S. military drills that the allies call routine but that North Korea claims are invasion preparations.
The Kaesong industrial park started producing goods in 2004 and has been an unusual point of cooperation in an otherwise hostile relationship between the Koreas.
North and South Korea do not allow their citizens to travel to the other country without approval, but an exception had previously been made each day for the South Koreans working at Kaesong.
About 120 South Korean firms run factories in the border town of Kaesong, with 53,000 North Koreans working there. Using North Korea's cheap, efficient labor, the Kaesong complex produced $470 million worth of goods last year.
Pyongyang threatened last week to shut down the park, which is run with mostly North Korean labor and South Korean know-how. It expressed anger over South Korean media reports that said North Korea hadn't yet shut the park because it is a source of crucial hard currency for the impoverished country.
In 2009, North Korea closed its border gate in anger over U.S.-South Korean military drills, leaving hundreds of South Korean workers stranded in Kaesong for several days. The park later resumed normal operations.
"I feel worried that I'm unable to do business and also feel anxious," Joe In-suk, a 54-year-old South Korean who had planned to travel to Kaesong on Wednesday, said at a border checkpoint in Paju, South Korea. About a dozen South Korean trucks were lined up at the checkpoint leading into North Korea.
If North Korea continues to deny entrance to South Korean workers, it could be tantamount to a shutdown because Kaesong factories cannot operate production lines without supplies of raw materials sent regularly by truck from the South to the North.
A South Korean manager whose company runs a factory in Kaesong was worried that buyers would drop future orders if North Korea continued to block workers and supplies from the South.
"For some companies, today's move must have already dealt them a blow," the manager said Wednesday, speaking on condition of anonymity because he wasn't authorized to talk
to the media. "We cannot produce goods without raw material."
Seoul's Unification Ministry urged Pyongyang to "immediately normalize" cross-border traffic in and out of Kaesong.
The U.S., meanwhile, called for North Korea to abandon its nuclear ambitions, saying it would be "extremely alarming" if Pyongyang follows through on a vow to restart its plutonium reactor.
White House spokesman Jay Carney said the U.S. is taking steps to ensure it has the capacity to defend itself and its allies.
But Carney noted that a string of threats from North Korea toward the U.S. and South Korea so far have not been backed up by action, calling the threats part of a counterproductive pattern. He called on Russia and China, two countries he said have influence on North Korea, to use that influence to persuade the North to change course.
U.S. Defense Secretary Chuck Hagel called North Korea's development of nuclear weapons a growing threat. In a telephone call Tuesday evening to Chinese Defense Minister Chang Wanquan, Hagel said Washington and Beijing should continue to cooperate on North Korea's pursuit of nuclear weapons and ballistic missiles.
China, North Korea's only major economic and diplomatic supporter, expressed unusual disappointment with its ally.
Hwang Jihwan, a North Korea expert at the University of Seoul, said the North "is keeping tension and crisis alive to raise stakes ahead of possible future talks with the United States."
"North Korea is asking the world, `What are you going to do about this?'" he said.
The North's nuclear statement Tuesday suggests it will do more to produce highly enriched uranium. The technology needed to make highly enriched uranium bombs is much easier to hide than huge plutonium facilities. North Korea previously insisted that its uranium enrichment was for producing electricity - meaning low-enriched uranium.
Kim Jin Moo, a North Korea expert at the Korea Institute for Defense Analyses in South Korea, said that by announcing it is "readjusting" all nuclear facilities, including the uranium enrichment plant, North Korea "is blackmailing the international community by suggesting that it will now produce weapons-grade, highly enriched uranium."
The North's plutonium reactor was disabled under a 2007 deal made at now-dormant aid-for-disarmament negotiations involving the North, the U.S., South Korea, Japan, China and Russia.
In 2008, North Korea destroyed the cooling tower at Nyongbyon in a show of commitment, but the deal later stalled after the North balked at allowing intensive international fact-checking of its past nuclear activities. North Korea pulled out of the talks after condemnation of its long-range rocket launch in April 2009.
North Korea is believed to have exploded plutonium devices in its first two nuclear tests, in 2006 and 2009.
There had long been claims by the U.S. and others that North Korea was also pursuing a secret uranium program. In 2010, the North unveiled to visiting Americans a uranium enrichment program at Nyongbyon.
Analysts say they don't believe North Korea currently has mastered the miniaturization technology needed to build a warhead that can be mounted on a missile, and the extent of its uranium enrichment efforts is also unclear. Some experts estimate North Korea may have enough plutonium for perhaps four to eight rudimentary bombs.
Associated Press writers Foster Klug, Hyung-jin Kim and Youkyung Lee in Seoul and Kim Yong-ho in Paju contributed to this report.