The medical aid group Medecins Sans Frontieres has pulled 16 staff out of a Sudanese rebel-controlled town in south Darfur after fierce fighting this week.
A number of rebel movements have threatened not to attend the talks
MSF said its staff left after patients fled the only hospital in Muhajiriya and mortar fire intensified on Tuesday.
The only Darfur rebel group to sign a 2006 peace accord blames the army for the assault and says dozens have died.
The Sudan Liberation Army (SLA) says it is now reviewing its relationship with the Sudan government.
MSF said the evacuation means that local people are now in urgent need of medical care.
Spokesman Seif Haroun for the faction led by Minni Minnawi told the BBC's Network Africa programme that it was still committed to attend peace talks in Libya later this month but warned that it would do whatever it could to protect its people.
The SLA had earlier said the fighting came as "a stab in the back" for their alliance with Khartoum.
The Sudanese government has denied involvement in the attack
The UN reports an upsurge of attack across a large number of locations in Darfur,
Amnesty International has warned that Sudan's Armed Forces are gathering in large numbers in at least six Darfuri towns.
The London-based human rights organisation said it had received credible reports that the Sudanese army was close to the towns of Kornoy, Um Baru, Kutum and Tine in northern Darfur.
A separate report spoke of a clash between soldiers and a rebel group in Tine, which is close to the Chadian border.
Observers say the upsurge in fighting is an attempt to gain ground ahead of the peace talks due on the 27 October, but the BBC's Amber Henshaw in Khartoum says this latest spate of violence does not bode well.
Intensive diplomatic efforts are underway to ensure the talks take place, with the United Nations Special Envoy for Darfur, Jan Eliasson conducting meetings in Khartoum following discussions with the AU over the last few days.
Mr Eliasson is holding talks with Sudanese officials as well as a number of regional governments, including Libya, Eritrea, Egypt and Chad.
At the same time rebel leaders are being airlifted to the southern Sudanese capital, Juba, to try to find a common position on Friday and Saturday.
The attack on the SLA-controlled town comes just 10 days after the African Union (AU) base in nearby Haskanita was raided by armed men, presumed at the time to be rebels.
Ten AU peacekeepers were killed in the raid, while equipment was destroyed or looted.
At least 200,000 people have died in Darfur during a four-year conflict and more than two million have been forced from their homes.