Darfur rebels claim government forces have launched more ground and air attacks on their positions and villages in North Darfur.
Two rebel groups say the attacks started on Saturday morning and that civilians are fleeing the area.
They say that government air assaults have struck the villages of Tarny and Khazan Tungur and other settlements in North Darfur east of Jebel Marra.
No one was immediately available for comment from the Sudanese Army.
The rebels say the air assaults were backed up with ground attacks and there has been heavy fighting since Saturday morning.
Commander Ibrahim Al-Hillo, from a faction of the Sudan Liberation Army headed by exiled leader Abdel Wahid Mohammed al-Nur, accused the government of indiscriminately attacking villages and civilians using the same tactics they used at the beginning of the conflict in Darfur.
A field commander from a separate group, the Sudan Liberation Army Unity Faction, said many civilians were fleeing the area.
He said the government had started this latest operation a week ago and had bombed villages in North Darfur every day.
A spokesman for the international peacekeeping mission in Darfur said they were investigating the reports.
On Friday the new joint African Union United Nations chief negotiator Djibril Bassole put out a statement saying he was "concerned" about reports of continued fighting in Darfur.
He urged all sides to "cease all military activities in order to protect civilians and create conditions for political dialogue".