South Korean workers began returning Saturday from a jointly run industrial park in North Korea after Seoul announced a complete withdrawal following months of military tensions.

The move plunges into doubt the future of the Kaesong complex -- once a rare symbol of cooperation across the world's most heavily militarized border, and a crucial source of hard currency for Kim Jong-Un's isolated regime.

North Korea said Saturday that it would put a U.S. citizen on trial for trying to overthrow the communist regime, in the face of soaring tensions between Pyongyang and the West.

The North's official Korean Central News Agency (KCNA) said U.S. citizen Pae Jun-Ho had admitted to the charges and would soon face "judgment.”

South Korea called Friday for the withdrawal of all remaining workers from its joint industrial complex with North Korea, after Pyongyang shunned an offer for talks on the zone's future.

"The government has made the inevitable decision to withdraw all the remaining people for their protection," the South's Unification Minister Ryoo Kihl-Jae told reporters.

The U.S.'s top military officer said in Japan Thursday that his troops were ready to act if North Korea turned its increasingly bellicose rhetoric into action.

"We are seeking to deter North Korea from provocation," General Martin Dempsey, chairman of the Joint Chiefs of Staff, told soldiers at the Yokota Air Base, about an hour's drive west of the Japanese capital.

South Korea on Thursday formally offered North Korea talks on suspended operations at their joint Kaesong industrial zone, and hinted it might pull out entirely if Pyongyang declines.

The South said it was offering working-level talks to resolve the impasse over Kaesong, a rare symbol of inter-Korean cooperation that has become the most notable victim of escalating military tensions on the Korean peninsula.

NATO foreign ministers condemned North Korea's war threats Tuesday, calling on it to abandon atomic weapons just as Pyongyang insisted it be treated as a nuclear-armed state on equal terms with long-time foe the United States.

"North Korea's provocative actions are in direct violation of U.N. Security Council resolutions and seriously undermine regional stability," the ministers said in a statement as they met at NATO HQ in Brussels.

Possible radioactive traces from North Korea's February nuclear test have been detected for the first time, although it remains unclear what fissile material Pyongyang used, monitoring organization CTBTO said Tuesday.

"The ratio of the detected xenon isotopes (xenon-131m and xenon-133) is consistent with a nuclear fission event occurring more than 50 days before the detection," the Comprehensive Test Ban Treaty Organization (CTBTO) said.

The wait for North Korea's expected missile test, which has kept South Korean and US forces on heightened alert for the past two weeks, may stretch to July, the South's defense ministry said Monday.

South Korean intelligence says the North has moved a number of ballistic missiles and missile launchers to its east coast in apparent preparations for a launch amid simmering tensions on the Korean peninsula.

North Korea has moved two more missile launchers to its east coast, where preparations are apparently under way for a missile test as tensions simmer on the peninsula, a report said Sunday.

Expectations had been high that Pyongyang would carry out a test to coincide with celebrations marking the birth of North Korea's late founding leader Kim Il-Sung on April 15 but it did not materialize.

The closure of the Kaesong joint-industrial zone has begun to hit deals between South Korean manufacturers and foreign buyers, Yonhap reported Saturday.

An Indian company has scrapped a deal with South Korean auto parts maker Daewha Fuel Pump Industrial Ltd after it failed to deliver parts because of the suspension of operations, the agency said.