Darfur's main rebel group says it has been attacked by Sudanese government forces, one day after they signed an agreement designed to lead to peace talks.

A spokesman for the rebel Justice and Equality Movement says government aircraft bombed rebel fighters Wednesday in the mountainous area of Jebel Marra.

They say ground forces also clashed with rebels further to the east.

The French news agency AFP says government officials confirmed the attacks.

Also Wednesday, a United Nations official said logistical issues have delayed the deployment of more peacekeepers to Darfur by several months. U.N. Undersecretary-General for Field Support, Susana Malcorra, said the mission is unlikely to reach full strength until the end of the year.

The mission currently has a little over 12,000 military personnel, which is only about 60 percent of what is expected to be the world's largest peacekeeping operation.

Speaking in Khartoum, Malcorra said the delays have no connection with political developments -- an apparent reference to the International Criminal Court proceedings against Sudanese President Omar al-Bashir.

Sudan has said Darfur peace efforts would be endangered if the ICC issues an arrest warrant for the president. The court's chief prosecutor, Luis Moreno-Ocampo accuses Mr. Bashir of orchestrating a genocide in Darfur.

U.N. Secretary-General Ban Ki-moon says Sudan must cooperate with the court and should ensure the safety of U.N. peacekeepers and Sudanese civilians.

The United Nations says more than 200,000 people have been killed in fighting or related violence since Darfur rebels began their uprising in 2003. Sudan says only 10,000 people have died as a result of the conflict.

Some information for this report was provided by AFP and AP.