The African Union has accused Sudanese government forces of supporting Arab militiamen targeting civilians in the troubled region of Darfur.
More than two million have fled their homes in Darfur
The head of the AU mission in Sudan said government helicopters gunships had flown overhead during a recent militia attack on a refugee camp.
But he suggested that rebels had also broken a truce signed by both sides.
About 180,000 people have been killed and two million have fled their homes since the conflict began in early 2003.
There has been an upsurge in violence in recent days.
On Wednesday at least 32 people died during an attack by pro-government Janjaweed militias on Aro Sharow refugee camp in western Darfur.
The head of the AU's peacekeeping mission in Sudan, Baba Gana Kingibe, told reporters that army helicopters had been flying overhead in an "apparent air and land assault".
He said this gave "credence to the repeated claim by the rebel movements of collusion between the government of Sudan forces and the Janjaweed".
Both sides blamed
Mr Kingibe also spoke of close co-ordination by Sudanese forces in militia attacks earlier in the month in north Darfur.
The head of the AU mission in Sudan said both sides in the conflict had violated the ceasefire.
Janjaweed militias are accused of widespread atrocities
"There is neither good faith nor commitment on the part of any of the parties," he said.
The Sudanese government denies any links to the Janjaweed and describes them as criminals.
United Nations Secretary General Kofi Annan on Friday condemned "attacks of civilians, humanitarian workers and assets and the African Union mission in Sudan".
Mr Annan called for those responsible to be brought to justice.
The conflict began in early 2003, after a rebel group began attacking government targets.
About 5,600 peacekeepers from the African Union are monitoring a ceasefire agreement reached in April 2004.