North Korea announced unilaterally Friday that all joint venture contracts with South Korea over the Kaesong industrial complex would be null and void, according to South Korean officials.

South Korean companies and officials in Kaesong must unconditionally accept what we notified them and, if unwilling, they can leave the complex, the North Korea said in a statement.

The South Korea government expressed deep regret at this announcement. The South Korea cannot accept such an unilateral and basic threat, said Kim Ho-Nyun, the South's Unification Ministry spokesman.

If the North unilaterally pushes through with this measure, all responsibility will rest with the North, he said.

The North Korea said last month it wanted South Korea businesses in the industrial zone to increase wages, now about 75$ a month for per worker, but it has not said how much. Friday's move was the latest in a series of steps by the North to disrupt operations at the complex.

Over the Kaesong Industrial Complex projects, there are near 100 South Korean companies that employ about 39,000 North Koreans. North Korean officials have been eager to get more money from South Korea, which cut off aid to the North a year ago to pressure it to end its nuclear-weapons program.

The South Korean government said earlier Friday it was seeking new dialogue with Pyongyang after the North's statement released.