South Koreans commuting to an inter-Korean industrial complex in North Korea's Kaesong crossed the border without a hitch on Thursday, despite the North's severance of a military hotline with the South on the previous day, officials said.

On Wednesday, Pyongyang, citing hostility from the United States and South Korea, abruptly cut off its western coastal military hotline with Seoul, which is responsible for guaranteeing the safety of South Korean personnel commuting to and from Kaesong, raising concern over the operation of the inter-Korean industrial complex.

A first group of 197 South Korean workers crossed the land border through the Immigration and Quarantine (CIQ) office in Paju, north of Seoul, at 8:30 a.m. after receiving entry approval by phone from a North Korean complex management office in Kaesong.

"The North gave the daily approval on the cross-border trip for South Korean workers by phone through the Industrial District Management Committee this morning," a CIQ official said.

The joint industrial park, home to about 120 South Korean companies, is believed to be one of North Korea's major hard currency income sources. South Korea needs approval from the North on the cross-border movement of South Korean workers in and out of the industrial zone.

A total of 530 South Koreans are scheduled to travel there on Thursday, while 511 people are scheduled to return to the South.

The North's severing of the emergency military communication line, designed to help prevent unexpected military skirmishes, was the latest in a series of continued military threats and provocations from the North. Two weeks ago, the communist country cut off the hotline managed by the countries' Red Cross groups.

Angered by joint South Korea-U.S. military drills in March and the United Nations' punitive resolutions adopted after its launch of a long-range rocket in December and a third nuclear test in February, the North has repeatedly threatened to take military actions against the allies, including "preemptive nuclear attacks." (Yonhap News)