Army generals and protest leaders had been expected to come to an agreement on Wednesday over the make-up of a new body to govern Sudan for three years.
The issue is the thorniest to have come up in ongoing talks on reinstating civilian rule after the generals took over following the ouster of longtime autocratic president Omar al-Bashir last month.
But in the early hours of Thursday, the chief of Sudan's ruling military council, General Abdel Fattah al-Burhan, announced the talks had been suspended for 72 hours due to deteriorating security in Khartoum.
He demanded that protesters dismantle roadblocks in Khartoum, open bridges and railway lines connecting the capital and "stop provoking security forces".
The Alliance for Freedom and Change, the group that is leading the protest movement and negotiating the transfer of power with the army rulers, called the move "regrettable".
"It ignores the developments achieved in negotiations so far...and the fact that Wednesday's meeting was to finalise the agreement, which would have stopped the escalations such as roadblocks," the alliance said in a statement.
The protest movement vowed to press on with the sit-in outside the army headquarters and across the country.
Several roadblocks removed
Protesters said the army aimed to provoke demonstrators. "They want to provoke the people by delaying the negotiations ... but the negotiations will resume now that the roadblocks have been removed," said Moatassim Sayid, a protester at the sit-in.
On Thursday morning, several roadblocks in downtown Khartoum had been taken down, an AFP correspondent reported, adding that troops from the paramilitary Rapid Support Force (RSF) were deployed in some areas.
Roadblocks on key thoroughfares in the capital are being used by demonstrators to pressure the generals to transfer power to a civilian administration.
The talks began this week and achieved significant breakthroughs, but have also been marred by violence that on Monday left five protesters and an army major dead, with many wounded from gunshots.
Protesters say members of RSF were behind the violence. But Burhan said there were "armed elements among demonstrators who were shooting at security forces."
He defended the paramilitary group, saying "it had taken the side of the people" during the uprising that toppled Bashir on 11 April.
US, UK say military to blame for ongoing clashes
Washington blamed the military council for Monday's bloodshed. "The tragic attacks on protesters ... were clearly the result of the Transitional Military Council trying to impose its will on the protesters by attempting to remove roadblocks," the US embassy said in a statement.
The British ambassador to Khartoum said Sudanese security forces had fired at protesters on Wednesday when eight were reported wounded near the sit-in, where thousands remain camped demanding the generals step down.
Extremely concerned by use of live ammunition by Sudanese security forces against protestors in Khartoum today, with reports of civilian casualties. After Monday’s awful violence and killings this is inexplicable. Military Council must act to stop this now. No more excuses.Irfan Siddiq (@FCOIrfan) May 15, 2019
"Extremely concerned by use of live ammunition by Sudanese security forces against protesters in Khartoum today, with reports of civilian casualties," Irfan Siddiq wrote on Twitter on Wednesday. "Military council must act to stop this now. No more excuses."