Beijing on Tuesday dismissed a UN report's warning that its officials could be complicit in alleged human rights violations by Pyongyang by forcibly repatriating North Koreans from China.

A 400-page United Nations report issued Monday detailed human rights violations including "extermination, murder, enslavement, torture, imprisonment, rape, forced abortions and other sexual violence".

The report by the Commission of Inquiry on Human Rights in the Democratic People's Republic of Korea also included "concerns relating to China's policy and practice of forced repatriation" of North Korean citizens.

The commission said it "expressed particular concern about Chinese officials providing specific information on such persons" to North Korean authorities.

It called on Beijing to "caution relevant officials that such conduct could amount to the aiding and abetting of crimes against humanity" in North Korea.

Foreign ministry spokeswoman Hua Chunying roundly rejected any Chinese complicity in human rights violations in the North.

"We totally don't accept this accusation," she said at a regular briefing.

"On the North Korean defector issue, our position is very clear," she said. "We properly deal with that in accordance with international law and humanitarian principles."

The report quoted a written reply by China as saying that North Korean "citizens who have entered China illegally do it for economic reasons" and are not refugees, a view reiterated by Hua.

China is the North's key ally and protector, providing badly needed trade and aid for fear that a collapse of the regime could unleash chaos across the border and allow the United States to bolster its presence in Asia.

Pyongyang, however, routinely defies Beijing's calls for calm, restraint and denuclearisation, pushing ahead with nuclear weapons tests and issuing apocalyptic threats against the United States and South Korea.