"The level of violence being faced by humanitarian workers in Darfur is unprecedented," Manuel da Silva, the United Nations humanitarian coordinator in Sudan said in a statement.
Ambushes and hijackings have increased and efforts to help people in refugee camps were suspended after three aid workers were beaten to death by a mob in the Zalinge area, the United Nations reported.
The government and one faction of the Sudanese Liberation Movement signed a peace agreement in May. But another faction refused to sign.
"Since the signing of the agreement, Darfur has become increasingly tense and violent, which has led to the tragic deaths of far too many civilians and aid workers," Oxfam's Paul Smith-Lomas was quoted as saying by the BBC. "A full and comprehensive cease fire must be implemented immediately."