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.

Dozens of South Korean trucks were already returning across the border earlier on Thursday, 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 (Democratic People’s Republic) of Korea H-bomb test and launch of a satellite,” the North’s committee for the peaceful reunification of Korea said, referring to South Korea.

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.

“South Korean enemy forces will experience themselves the harsh and painful price they should pay for halting the Kaesong industrial complex,” North Korea said on Thursday.

“We seize all assets of the South Korean companies and related organisations including machinery, raw materials and goods,” it said.

Except for Kaesong, both countries forbid their citizens from communicating with each other across the world’s most fortified frontier.

“We piled up instant noodles, bread and drinks in our warehouse so North Korean workers could come here and eat freely,” said Lee Jong-ku, who runs a firm that installs electrical equipment for apparel factories in Kaesong. “We don’t mind them eating our food, because we only care about them working hard.”