A spokesman for the main rebel faction group said that despite a peace agreement signed on May 5, heavy attacks have continued on the ground.
"The attack on Shearia was yesterday - the Janjawid have attacked many many places in South Darfur despite the peace deal," al-Tayyib Khamis said on Saturday.
"There are about 20 to 25 dead and many injured but it's unclear as yet how many."
The government and the Minni Arcua Minnawi faction group signed a peace deal in Abuja under foreign diplomatic pressure. But two other factions at the talks did not sign, saying it was not fair. Thousands of Darfuris have since been demonstrating against the agreement.
Arab militias, known locally as Janjawid, were not part of the peace talks in Abuja. The United Nations said that because Khartoum armed them to fight the mostly non-Arab rebels, the government therefore represented them.
Khartoum admits arming some tribes to fight the rebels but denies links to the Janjawid, saying they are outlaws.
The African Union, with a 7,000-strong force monitoring a widely ignored ceasefire in the region, was unable to confirm the fighting in Shearia.
Shearia is a flashpoint of violence in Darfur as Arab nomadic tribes clash with non-Arab rebel commanders who often use civilian villages as their bases in the region.
Infighting between rebel factions is also common as the boundaries of areas of control are fluid.