Sudans military has unleashed a volley of gunfire and burnt down tents, killing at least 30 people, according to witnesses and protest leaders.
The violence comes after the ruling military moved to crush the protest movement opposing its grip on power, as security forces overran the main sit-in site in the capital.
For months, protesters have camped outside the militarys headquarters, as the two sides negotiated over who would run the country after the April removal of long-time leader Omar al-Bashir.
After succeeding in forcing the military to remove al-Bashir, the protesters stayed in the streets, demanding the generals move to the background and allow civilians to lead the transition.
Scattered by the bloody assault, protesters vowed to keep up their campaign, suspending talks and calling for a general strike and civil disobedience.
They urged night-time marches across the country.
This is a critical point in our revolution. The military council has chosen escalation and confrontation, said Mohammed Yousef al-Mustafa, a spokesman for the Sudanese Professionals Association, which has spearheaded the protests.
Those are criminals who should have been treated like al-Bashir, he said.
Now the situation is either them or us, there is no other way.
The ruling military council said in a statement that security forces had been trying to clear an area next to the protest camp, when those it was chasing fled into the sit-in site, leading to the shooting deaths and injuries.
But activists said the assault appeared to be a co-ordinated move, with other forces attacking similar sit-ins in Khartoums sister city of Omdurman and the eastern city of al-Qadarif.
The attack came on the day before the festival of Eid, which marks the end of Ramadan, the holy month when Muslims fast during daylight hours.