Sudan’s security forces stormed a major protest camp in the nation’s capital of Khartoum on Monday, killing an estimated 31 people and wounding hundreds, protest organizers said, in a day of violence that plunged the country’s once-hopeful revolution into chaos and uncertainty.

The dawn raids, led by a paramilitary unit notorious for atrocities in the western region of Darfur, appeared to signal that the military was intent on breaking the pro-democracy movement that galvanized Sudan following the ouster in April of the longtime dictator and president Omar Hassan al-Bashir.

Soldiers fanned out across the city from first light, opening fire on protesters, burning their tents and thrashing civilians with sticks. The brutal crackdown came days after the collapse of power-sharing negotiations between civilian and military leaders over who should run Sudan during a planned transitional period.

On Monday that transition was cast into doubt as Sudan lurched toward the kind of bloody authoritarianism that quashed the Arab Spring in 2011. The crackdown confirmed protesters’ fears that Sudan’s military, backed by the wealthy rulers of Saudi Arabia and the United Arab Emirates, was never serious about its claims to support civilian rule.