North Korea said it was kicking out all South Koreans from the jointly run Kaesong industrial zone on Thursday, calling the South's move to suspend operations, in retaliation for Sunday's rocket launch by the North, a "declaration of war".

The North declared the industrial park, run by the rivals as a symbol of cooperation for more than a decade, a military control zone, the agency that handles its ties with Seoul said, according to the official KCNA news agency.

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Dozens of South Korean trucks were already returning across the border earlier in the day, laden with goods and equipment, after the South said it was pulling out.

"Unpardonable is the puppet group's act of totally suspending the operation in [Kaesong], finding fault with the DPRK's H-bomb test and launch of a satellite," the North's Committee for the Peaceful Reunification of Korea said, referring to South Korea.

Isolated North Korea regularly dismisses the South as a puppet of the United States and just as regularly accuses both of acts of war against it.

DPRK is short for the North's official name, the Democratic People's Republic of Korea. North Korea tested what it said was a hydrogen bomb on Jan. 6 and on Sunday launched a rocket, putting a satellite into orbit.

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The United States, Japan and South Korea said Sunday's launch was a ballistic missile test, and like last month's nuclear test, a violation of U.N. resolutions. The U.S. Senate voted unanimously in favor of tougher sanctions.

North Korea ordered South Koreans out of the zone by late afternoon, forbidding them to take anything other than personal belongings, KCNA said. South Korea said after the North's announcement that its top priority was the safe return of all of its people.

Halting activity at the park, where 124 South Korean companies employed about 55,000 North Koreans, cuts the last significant vestige of North-South cooperation – a rare opportunity for Koreans divided by the 1950-53 war to interact on a daily basis.

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North Korean workers were given a taste of life in the South at the complex, about 34 miles northwest of Seoul, including snack foods like Choco Pies and toiletries that were resold as luxury items in the North.

They also rubbed shoulders with their managers from South Korea. Supporters of the project said that kind of contact was important in promoting inter-Korean understanding, despite concerns that Pyongyang might have used proceeds from Kaesong to help fund its nuclear and missile programs.