North Korea has resumed its indoctrination of South Korean abductees as part of a broader effort by the reclusive regime to tighten control over its people, a local activist group said Monday.

According to the Abductees' Family Union that cited sources with contacts in North Korea, Pyongyang has resumed its ideological brainwashing of South Korean prisoners of war, their families and people the regime kidnapped over the years.

It said that the first indoctrination courses took place last year after a hiatus of some 30 years.

Painting of a North Korean propaganda (Yonhap)There are presently estimated to be some 500 POWs and abductees living in North Korea, although Pyongyang has refuted their existence. 

"The latest indoctrination training comes with the Ministry of People's Security taking charge of summoning POWs and their families and other former South Koreans living in the country so they can be mentally fortified," the union's chief Choi Sung-yong said.

He also said that there has been a move by authorities to tighten surveillance against people from the South.

Up until 1986 the North operated special camps where prisoners taken during the 1950-53 Korean War and those kidnapped after the conflict were gathered together in places like Pyongyang and Wonsan so they can be indoctrinated. 

The union, dedicated to finding people kidnapped by the North, said in the past sessions that lasted months, the regime focused on highlighting the virtues of the North Korean political system and the glories of its leaders.

"The sudden resumption may be closely linked to the recent increase in people escaping the North and may be aimed at preventing those who are most likely to defect from doing so," an anonymous insider of the group said. (Yonhap)