North Korea has barred South Korean workers from entering a jointly run factory park just over the heavily armed border in the North, officials in Seoul said.
The move came a day after Pyongyang announced it would restart its dormant plutonium reactor and increase production of nuclear weapons material.
The bid 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.
It has threatened to stage nuclear and missile strikes on Seoul and Washington and 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 nationals who planned to travel to the park yesterday were being refused entry.
He said North Korea cited political circumstances on the peninsula when they delivered their decision to block South Korean workers from entering Kaesong.
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 peninsula is technically in a state of war because the Korean War ended in a truce, not a peace treaty. The North is angry about South Korea-US military drills and new UN sanctions over its February 12 nuclear test.
Dozens of South Korean firms run factories in the border town of Kaesong.