Kidnapped men have been forced to work on farmland controlled by Janjaweed militias, a coalition of African charities says.
Eyewitnesses also say the Sudanese army has been involved in abducting women and children to be sex slaves and domestic staff for troops in Khartoum.
But Khartoum said the report was "very naive" and called the authors ignorant.
"The government does not condone abductions and it is not government policy," a government spokesman told the BBC.
"We are working hard to stop such violations. The rebel factions are mostly to blame for abductions in Darfur." Up to 300,000 people have died since conflict began in Darfur in 2003 and at least 2.7 million people have fled their homes.
Thousands of people from non-Arabic speaking ethnic groups in Darfur have been targeted, says the report, published by the Darfur Consortium on Wednesday. continue reading here