Seoul prosecutors have arrested a South Korean accused of hunting North Korean refugees in China and sending them back to their communist homeland, a report said Monday.

The man is also accused of collecting information on people helping the refugees as well as military information for the North, officials at the Seoul Central Prosecutors' Office were quoted by Yonhap news agency as saying.

They said the 55-year-old identified only as Kim was recruited by a North Korean agent while staying illegally in China in the late 1990s.

He reportedly visited Pyongyang in 2000 for spy training and was sent back to China as an agent searching for refugees.

Kim recently returned to South Korea after an accomplice was arrested by Chinese police and jailed. Prosecutors took him into custody upon arrival, Yonhap said.

Prosecutors and the National Intelligence Service (NIS) are expanding their probe to see if Kim had more accomplices involved in espionage, officials were quoted as saying.

The prosecutors and the NIS said they could not immediately confirm the report.

Almost all those fleeing hunger or repression in North Korea cross the border to China. Some travel on to Southeast Asian nations in hope of eventual resettlement in South Korea, because Beijing has an agreement with Pyongyang to repatriate those refugees it catches as economic migrants.

Refugee and rights groups strongly criticise China's policy, saying the returnees face harsh punishment back in their homeland.

Almost 18,000 North Koreans have arrived in South Korea since the 1950-1953 war.

The South's anti-communist National Security Law bans citizens from contacting North Koreans without government approval and punishes activities benefiting the North.