BEIJING (AFP) - China on Monday angrily rebuked a UN agency which criticised it over the repatriation of nine young North Korean refugees who had fled to Laos.

The nine, detained in the South-east Asian country more than three weeks ago, were sent to China on Monday last week and flown back to North Korea the following day.

The UN's human rights and refugee agencies on Friday took China and Laos to task over the incident, prompting a reaction from China's foreign ministry.

"We hope that the Office of the High Commissioner for Human Rights of the UN does not make irresponsible remarks based on unspecified news," foreign ministry spokesman Hong Lei told a regular briefing.

On Friday Rupert Colville, spokesman for the UN rights office, expressed concern for the safety of the North Koreans whom he said "are at risk of severe punishment and ill-treatment".

China also appeared to attempt to distance itself from the repatriation, saying the refugees had passed through the country with "valid documents and visas".

"In the whole process, China has not received a request by any party to assist in the repatriation of these persons," Hong added.

North Korean refugees traditionally try to make the journey to South Korea by first heading to China and then proceeding onwards from other countries, including some in Southeast Asia.

Laos previously had been seen as a relatively safe transit point.

North Korean leader Kim Jong Un is believed to have tightened border controls since he came to power after the death of his father Kim Jong Il in December 2011.