The Sudanese government together with the Janjaweed militia have launched new attacks in northern Darfur, the African Union (AU) has said.
African Union troops are overstretched in Darfur
The AU said the ground and air offensive was a flagrant violation of security agreements.
It said there had been a heavy toll on a civilian population. Rebels in the area said 70 people had died.
Earlier, Sudan welcomed the UN's support for AU peacekeepers in Darfur but denied the UN will take command.
The AU said in a statement that Birmaza, a much fought over village in Darfur, had been subject to ground and aerial assault.
The statement said there had been heavy casualties among the civilian population, but gave no figures.
Rebels in the area said the government troops and Arab militia were continuing on Saturday to burn villages and loot cattle.
So far there has been no official reaction from the government in Khartoum.
'No UN troops'
The AU statement comes only days after the Sudanese government welcomed the UN's support to strengthen the AU peacekeeping mission in Darfur.
UN Secretary General Kofi Annan said on Thursday after talks on Darfur in Ethiopia's capital, Addis Ababa, that a compromise had been reached for a hybrid UN-AU force in Sudan's western region.
But Sudanese Foreign Minister Lam Akol said shortly afterwards that "there should be no talk about a mixed force" and that there would be no UN troops in Darfur.
Mr Akol said that the UN would simply provide technical support.
Khartoum has always rejected plans to replace the AU force with a larger, stronger UN mission.
Violence has intensified despite a peace deal in May between the government and one of the Darfur rebel groups.
UN humanitarian chief Jan Egeland has cut short his trip to Darfur after Sudan's government told him it would be too dangerous for him to travel outside the region's major towns.
Mr Egeland said on Saturday the international community should not drag its heals over implementing the Darfur deal, warning that more people would die in the region.
He said that leaders "from all over the world... swore to protect civilian populations. We have a responsibility to protect. We are not living up to that responsibility in Darfur today.
"I met... yesterday women [in Darfur] who were pleading for security, who said we are abused, we are raped, we are attacked and nobody seems to want to protect us," Mr Egeland said.
A further possible area of disagreement on the peacekeeping mission is the size of the new force.
The UN also wants a force of 17,000 troops, while Sudan says 12,000 would be enough.
The conflict has killed or displaced hundreds of thousands of people
There are currently some 7,000 AU troops in Darfur.
Sudan has always said that the problems in Darfur are being exaggerated for political reasons.
It denies backing Arab Janjaweed militias, which are accused of genocide against Darfur's black African population.
Sudan says the militias are being disarmed but reports from Darfur say the army is working with the Janjaweed to destroy villages.
More than 200,000 people have died in three years of conflict in the region.
About three million have fled their homes.