The African Union has suspended Sudan's membership "with immediate effect", amid an upsurge of violence in the capital that has seen dozens killed.
The pan-African body has warned of further action if power is not transferred to a civilian authority - a key demand of pro-democracy protesters.
Opposition activists say a paramilitary group has killed 108 people this week, but officials put the figure at 46. Residents said pro-government militia were all over the capital Khartoum.
The violence intensified on Monday when security forces stormed a weeks-long sit-in outside military headquarters in the capital. It is the deadliest incident since veteran President Omar al-Bashir was ousted by the military in April after months of peaceful protests.
Talks between opposition activists and the ruling interim military council have since broken down.
"The AU Peace and Security Council has with immediate effect suspended the participation of the Republic of Sudan in all AU activities until the effective establishment of a Civilian-led Transitional Authority, as the only way to allow the Sudan to exit from the current crisis," the AU tweeted on Thursday.
The decision was made unanimously by members at an emergency meeting of the AU in Addis Ababa that lasted more than five hours.