Abd al-Wahid Muhammad Ahmad Nur, chairman of the Sudan Liberation Movement (SLM), said in a statement on Sunday that peacekeepers should replace AU observers sent only to monitor a ceasefire agreed upon in April.
African leaders were meeting in the Nigerian capital, Abuja, on Sunday, with the Darfur conflict a major agenda item.
The humanitarian coordinator of the SLM, Sulayman Adam Jamus, accused government forces of violating a much-abused ceasefire by bombing two villages on Saturday in South Darfur state, southeast of its capital Nyala.
He said all 450 villagers fled their homes, which were burned to the ground. One person was killed, six were wounded and many were still missing, he added. AU officials said they were checking the reports.
After years of tribal conflict over scarce resources in arid Darfur, the SLM and the rebel Justice and Equality Movement took up arms in February 2003, complaining of discrimination and harassment of African villagers by the Arab militias.
Darfur's fighting has displaced up
to two million people since 2003
The government says it recruited militias to fight the rebellion but not the Janjawid, which it calls outlaws.
Two million people have fled their homes since early 2003, mostly to camps near towns and some to Chad.
A UN spokesman said on Friday that the Sudanese air force last week bombed the town of Shangil Tobaya, near al-Fashir, capital of North Darfur, killing or wounding 100 people and forcing thousands to flee.
Sudan said on Sunday that it was reviewing the UN report and promised to punish the troops if it were true.
The UN and AU - which is monitoring a shaky ceasefire deal - said the bombing violated the pact.
'Forced to respond'
"We have formed an investigation committee to find out what happened and if there was a bombing," Sudanese Interior Minister Abd al-Rahim Muhammad Husayn said on a visit to Dubai.
"Armies all over the world have committed mistakes and it is possible that an isolated bombing took place. If this is so, we will punish the offenders."
Darfur separatists say Khartoum
has violated the ceasefire again
Husayn insisted Sudan was abiding by the ceasefire and accused rebels of violating the accord "more than 200 times".
"Sudanese forces don't initiate any attacks but are forced to respond to any firing from rebels. We have handed over to the African Union a map of where all our armed forces are positioned but the rebels haven't done so until now," he said.
In a separate development, witnesses said Sudanese police and troops went on a rampage in ethnic Beja parts of Port Sudan on Saturday after shooting dead 18 people preparing to take part in a demonstration.
At least seven people were seriously wounded in the rampage in the Red Sea city in eastern Sudan, in which soldiers threw hand grenades into houses several miles from the scene of the demonstration, according to the witnesses.
"We have formed an investigation committee to find out what happened and if there was a bombing"
Abd al-Rahim Muhammad Husayn,
Sudanese interior minister
Abd Allah Musa Abd Allah, a prominent Beja politician, said dozens of houses were attacked but could not give a figure for the number of casualties.
Hospital sources said at least 18 people were killed and 40 injured in the shooting at demonstrators who had gathered for a march to demand that the Khartoum government start negotiations with the Beja on sharing power and the country's resources.
Beja organisations presented a list of demands last Wednesday and were preparing the demonstration on Saturday morning when troops opened fire at them, witnesses said.
The interior ministry declined on Saturday to comment on the number of people killed but said "a number of civilians tried to create a state of chaos ... and the police forces moved to challenge them."