Up to 50,000 residents have been killed and many more driven from their homes.
The UN also accused the government of using helicopter gunships in Darfur. Sudan denies the charges and insists it is improving security in the region.
The government says it has sent thousands of extra troops to Darfur in an effort to rein in militiamen and protect civilians.
But the report by Human Rights Watch says the government’s assurances are not credible.
The accusations of fresh atrocities come as a senior UN official begins a visit to Sudan’s neighbour, Chad, amid concerns about 200,000 Sudanese refugees there.
Many are without adequate shelter and roads have been closed as a result of recent heavy rains.
Humanitarian relief supplies are unable to reach the biggest camp, Breidjing.
