SEOUL, SOUTH KOREA (CBS NEWS) -- 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 bar South Koreans from entering the Kaesong factory park, 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 is allowing South Koreans to return home from Kaesong, but that about 480 South Koreans who had planned to travel to the park Wednesday were being refused entry.
"Our government regrets that today's situation, that the transit to the Kaesong industrial zone, was not normal," Kim, according to Reuters.
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.
The two sides do not allow their citizens to travel to the other country without approval, but an exception has previously been made each day for the South Koreans working at Kaesong.
The Korean Peninsula is technically in a state of war because the Korean War ended in a truce not a peace treaty.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.
Dozens of South Korean firms run factories in the border town of Kaesong. 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 wouldn't 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.
The move comes several hours after U.S. Secretary of State John Kerry met with his South Korean counterpart, Yun Byung-se, to underscore their alliance and demand North Korea put an end to its threats and nuclear ambitions.
"The United States will defend our allies and that we will not be subject to irrational or reckless provocation," he said. Earlier, North Korea vowed to restart its Yongbyong nuclear reactor, which can make one bomb's worth of plutonium a year.