SEOUL: North Korea has publicly executed four refugees who were repatriated by China and sent 40 others to its notorious prison camps, a South Korean activist said Monday.

China has repatriated 44 fugitives from its communist neighbor in recent months, said Kim Heung-Kwang, who heads NK Intellectuals Solidarity, a Seoul-based defectors' group.

Four of them were executed and 40 sent to camps for political prisoners, he told a seminar. South Korean rights groups say there are six political prison camps in the North holding around 200,000 detainees.

Kim said he had obtained his information from a source inside the North, but gave no details. The South's unification ministry, which is in charge of cross-border affairs, declined to comment.

Tens of thousands of North Koreans looking to escape hunger or repression in their communist homeland have fled in recent years. Virtually all cross the border to China, which repatriates those fugitives it catches.

Beijing says they are economic migrants rather than refugees, a policy criticised by international rights groups.

The refugees often travel on from China to southeast Asian countries, hoping to fly from there to South Korea. Last week 19 refugees were arrested in Thailand on charges of illegal entry.