South Korea warned on Wednesday that it would respond with decisive action if Pyongyang once again blocked access to a joint factory park in North Korea.
The government did not say exactly what measures it would take, but it did say that it was not yet considering shutting down the Seoul-funded Kaesong industrial park.
On Tuesday, North Korea lifted a blockade of border traffic that left hundreds stranded in the industrial park and nearly dried up supplies and materials for factories there.
The Kaesong complex lies just across the border from South Korea and is run by South Korean companies using cheap North Korean labor. North Korea has shut the border several times in recent days, preventing South Koreans from leaving or entering Kaesong.
Pyongyang is angry at the U.S. and South Korea for holding military exercises this month. The North says the exercises are a rehearsal for an invasion.
Since South Korean President Lee Myung-bak took office last year, North Korea has steadily scaled back operations at the zone in response the president's policies.
Pyongyang labels Mr. Lee a "traitor" for making South Korean assistance to North Korea contingent on the North ending its nuclear weapons program. The Kaesong complex is the only remaining joint project between the two Koreas.
Some information for this report was provided by AFP, AP and Reuters.