North Korea said it was kicking out all South Koreans from the jointly run Kaesong industrial zone on Thursday and freezing the assets of companies operating there, calling the South's move to suspend operations 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 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.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.Despite volatile North-South relations over the years, Kaesong had been shut only once before, for five months in 2013, amid heightened tensions following its third nuclear test. Its future had often seemed uncertain over the past decade.