Medecins du Monde, or Doctors of the World, has "suspended its activities in Darfur for an undetermined period of time," said the group's director of international missions, Eric Chevallier, in a phone interview.
"The balance between the help we were able to provide and the risks our staff were taking had reached breaking point," Chevallier said.
Meanwhile, the African Union chose Ghana to head the 53-member bloc Monday, turning aside Sudan's bid for the second year in a row because of the worsening violence in Darfur.
"By consensus vote President (John) Kufuor of Ghana has been elected to the presidency of the African Union," Alpha Oumar Konare, the A.U.'s chief executive, told reporters in the Ethiopian capital, Addis Ababa.
Also, new U.N. Secretary-General Ban Ki-moon called on African leaders Monday to help end worsening violence in Darfur by backing the urgent deployment of a joint U.N. and African peacekeeping force.
In a keynote speech at the opening of an African Union summit in Ethiopia, he said leaders should work together to end the deadlock that has held up the deployment of troops to the violence-wracked western Sudan region.
Ban also called for aid workers to be allowed to operate in Darfur as humanitarian agencies warned their operations are on the brink of collapse.
Six international charities other than Medicins du Monde said in a statement their aid work soon will be paralyzed unless urgent action is taken to end the rising violence.
"We must work to end the violence and scorched earth policies adopted by various parties, including militias, as well as the bombings which are still a terrifying feature of life in Darfur," Ban told African leaders including Sudanese President Omar al-Bashir. "The toll of the crisis remains unacceptable."
"Aid workers are facing violence on a scale not seen before in Darfur, leaving access to people in need at the conflict's lowest point," said the joint statement issued by Care International, the British Oxfam, the Norwegian Refugee Council and three other groups.
Doctors of the World is the first major aid group to pull out. Established in 1980, it runs medical missions in various African and Asian countries, but the mission in Darfur was one of the largest, with several million dollars spent on it annually since it was established in 2004.
"More than 200,000 people have been killed in fighting between government-backed militias, Sudanese troops and rebel groups. Two million people have been displaced, and women and girls attacked when they leave their camps to search for firewood. Female aid workers, too, are often targets," says CBS News reporter Katherine Arms.
The French aid group has begun pulling out more than a dozen international aid workers and some 200 Sudanese nationals working in the region, its international director said.
"It's a very difficult decision, and we hope we will be able to go back in when security improves," said Chevallier.
The aid group had been assisting some 90,000 refugees in the Kalma refugee camp of South Darfur, and had operated a mobile clinic treating about 30,000 people in remote villages in the Jebel Marra mountains where there was an outbreak of cholera last year.
He blamed the spiraling violence on all parties in Darfur, where multiple rebel groups fight the Sudanese army and the janjaweed paramilitary groups.
Chevallier said vehicle hijacking was making it impossible for the aid group to reach the remote villages where their aid is most needed, and that increased violence made it dangerous for staff to remain even in Darfur major towns. He pointed to a raid of four refugee compounds in the Gereida refugee camp on Dec. 18 during which a female aid worker was raped and several others endured mock executions while their vehicles and possessions were stolen.
"We decided it was better to leave before facing a serious problem than afterward," Chevallier said.
Attacks against civilians increased this month, killing 350 people and chasing tens of thousand more people from their home in January alone, the statement said.
The United Nations blames the Sudanese government in Khartoum for the brunt of the atrocities in Darfur, but the aid groups pointed out that "splits in the rebel movements and a widespread lack of accountability" is largely contributing to their worsening situation.
Ten AU peacekeepers have been killed since the African Union deployed in Darfur in June 2004, and the African mission says it needs more international support to pacify this region nearly the size of Texas.
Sudan opposes a U.N. Security Council resolution for some 22,000 U.N. peacekeepers to replace the overwhelmed African force, but Sudanese President Omar al-Bashir is due to discuss a compromise deal for a mixed U.N. and AU force with Secretary General Ban Ki-moon this week.
The U.N. says Darfur is the largest ongoing humanitarian operation in the world, with some 15,000 aid workers — including more than 1,000 expatriates — deployed in the region.
Sudan had been due again to assume the rotating AU presidency, after being forced to step aside because of Darfur.
"Awarding Sudan the chairmanship would not only reward the sponsors of crimes against humanity in Darfur, it would irreparably discredit the A.U.," said Peter Takirambudde, Africa director at the international watchdog Human Rights Watch, before the vote.