The only international aid group in a Darfur town where rebels reported that dozens of people were killed in a government attack said Wednesday it has pulled out for security reasons.

Doctors Without Borders said it could not confirm the deaths but counted at least 39 seriously wounded people _ mostly civilians _ in the South Darfur town of Muhajeria before it had to evacuate.

”There were casualties reported to us, but we couldn’t verify them,” said Banu Altanbas, a representative of the Paris-based group.

A U.N. observer in Darfur said Mahalya Arab tribesmen led the attack Monday, but could not say whether they had been sent by the government. The Sudanese army denied involvement, describing the clashes as intertribal battles.

Rebels said Sudan’s army and allied Arab militias pulled ethnic African tribal leaders out of a mosque and executed them before burning down half the town.

Sudan’s government has long been accused of using Arab militias known as the janjaweed in its fight against Darfur’s ethnic African rebels. The government denies backing the militias, which have been accused of the worst atrocities in four years of fighting that has left more than 200,000 people dead.

Altanbas said Muhajeria was too insecure to fully inspect, and that most civilians had taken refuge in its northern part, close to a small base of African Union peacekeepers who were treating some of the wounded.

The AU said it sent an inspection team to the town Wednesday, but could not yet confirm casualty tolls.

Altanbas said the town had been heavily damaged and that the area around the market place had been looted.

”Our hospital was completely empty, people have fled for fear of their lives,” she told The Associated Press by telephone from Nyala, South Darfur’s state capital.

She said all 16 of her group’s staff had evacuated the town.

The U.N. has advised nonessential staff from aid groups and U.N. agencies to temporarily leave Nyala because of increased insecurity there as well. But Doctors Without Borders said it was staying, and would try to return to Muhajeria as soon as possible.

Officials from the 7,000-member AU peacekeeping mission in Darfur said aircraft were circling above Muhajeria during the attack, but could not confirm rebel reports of aerial bombings. Sudan’s military spokesman, Brig. Osman Mohamed al-Aghbash, said in a statement the planes were conducting a reconnaissance operation approved by the AU.

Several U.N. resolutions ban military flights over the region, and the military denies it conducts aerial bombings. But many villages in the rebel zones are scarred by bomb craters, and the government is the only warring party in Darfur with aircraft.

The attack on Muhajeria is the latest threat to peace talks scheduled later this month in Libya. The town was controlled by the Sudan Liberation Movement, the only rebel group that has signed a peace agreement with the government.

Last week, the nearby town of Haskanita was razed after government troops took control following a rebel attack on an AU base that left 10 peacekeepers dead.

The Sudan Liberation Movement’s leadership says it is meeting to decide how to react to the aggression. Other rebel factions have increasingly expressed skepticism of the government’s sincerity in peace talks, and have warned that the army is massing in northern Darfur for another possible offensive there.

Rebels say the area around the town of Muhajeria is home to 160,000 people. Aid workers put the figure closer to 20,000 and 30,000.

In recent months, however, the area has seen a large influx of refugees fleeing attacks from government and militia forces.