Rebel commanders in the troubled Darfur region of Sudan say government aircraft have bombed northern areas of the province, in breach of a ceasefire.
The AU's 7,000 peacekeepers on the ground have made little impact
They said three villages had been hit over the weekend. African Union troops are investigating the claims.
The Sudanese government has denied the reports, which come days after President Omar al-Bashir vowed to adhere to a UN peace plan.
More than 200,000 people have died and 2.5m have fled their homes in Darfur.
A rebel commander, Abdallah Banda, from the rebel Justice and Equality Movement, said three villages had been destroyed by Sudanese aircraft in north Darfur.
He did not say how many people had died.
The Sudanese army denied the allegation.
"We never bombard civilians anywhere," a military spokesman told the Associated Press news agency.
Earlier this month a UN envoy said President Bashir was fully committed to a UN plan to send a hybrid UN and African peacekeeping force to Darfur.
A peace agreement was signed last May between the government and one leading rebel group but violence has continued, with rival rebels refusing to sign.
Some 7,000 African Union troops already on the ground have not been able to stop the violence - mostly blamed on pro-government Arab militias.
The Darfur conflict began in 2003 after a rebel group began attacking government targets, saying the region was being neglected by Khartoum.