The rebel group was not identified, nor was the number of casualties released.

A spokesman for the African Union, which is monitoring a fragile ceasefire between government-sponsored militias and Darfur rebels, said it had "no evidence" to support the allegations.

"An investigation is still going on," added Noureddine Mezni.

The UN Security Council passed a resolution last week demanding that the International Criminal Court prosecute those behind Khartoum's two-year-old scorched earth campaign against ethnic minority rebels in Darfur.