North Korea has been reinforcing the ideological education for its workers dispatched to China to prevent defections, a U.S.-based media report said Thursday.

An ethnic Korean source in China told Radio Free Asia that many North Korean workers employed in China came back to their job sites in the Chinese border city of Dandong after receiving indoctrination for about three days in North Korea's border city of Sinuiju.

According to the source, many North Korean residents are employed at Chinese businesses using the North Korea-China visa waiver accords, under which North Koreans are able to stay in China for 30 days without a visa.

In the past, North Korean workers in China went to Sinuiju when their visa-free period terminated and came back to Dandong after staying one or two days in the North, the source said.

"But recently, they returned to their workplaces in China after staying about three days in their country," the source told RFA.

"The reason for their prolonged stay in Sinuiju is that they got reeducation conducted by the North Korean public security authorities before they returned to China," the source claimed.

When North Korean workers arrive in border cities like Sinuiju they are sent to a special camp totally cut off from the outside world to receive ideological education.

Another source who declined to be identified said that Chinese employers have many complaints about their North Korean workers who are absent from work for several days.

"Nevertheless, Chinese firms using North Korean workers have no choice other than to wait until they return because of the cheap labor cost," the source said.

The insider said the ideological education is a measure to prevent a stream of defections of North Korean laborers overseas, like the recent case of North Koreans working at state-owned restaurants defecting en masse to South Korea on two separate occasions.

A group of 13 North Koreans defected from a Pyongyang-run restaurant in China and came to South Korea in early April in what has become a steady stream of people leaving the isolated country.

North Korea has consistently claimed South Korea abducted the workers and demanded that they be returned to their loved ones at once. Pyongyang also threatened to take strong actions against the South if its demands are not met. (Yonhap)