Rights group Amnesty International has accused China and Russia of breaching a United Nations arms embargo by letting weapons into Sudan that were then used in the Darfur region.
An Amnesty report published Tuesday expresses dismay that two permanent members of the U.N. Security Council were allowing weapons to flow into Sudan.
Russia and China have dismissed the allegation.
Amnesty International urged the U.N. to strengthen the existing arms embargo on Darfur.
The Amnesty report also accuses the Sudanese air force of operating airplanes and helicopters painted white to resemble U.N. aircraft. A U.N. report that was leaked to the media last month found that Sudan was using disguised airplanes to carry out bombing raids in Darfur. Sudan rejected the charge.
More than 200,000 people have been killed in Darfur since rebels began an uprising against Sudan's central government in early 2003.