Sudanese protest leaders canceled planned talks with the country's ruling generals on Tuesday as they visited a town where five teenaged protesters were shot dead.
Sudan's military ruler condemned the killing of the schoolchildren in the central town of Al-Obeid on Monday as the United Nations called for an investigation into what protesters said was a "massacre".
Demonstrators accused paramilitaries of the Rapid Support Forces of shooting dead the teenagers at a rally against shortages of bread and fuel.
The killings came as protest leaders were to hold talks with generals on Tuesday on the remaining aspects of installing civilian rule after the two sides inked a power-sharing deal earlier this month.
But two protest leaders who are members of the protest movement's negotiating team said the dialogue would not take place as planned.
"There will be no negotiations today as we are still in Al-Obeid," Taha Osman, a negotiator from the protest movement told AFP by telephone from the town.
"There will be no negotiation today with the Transitional Military Council as our negotiating team is still in Al-Obeid and will return only tonight," another negotiator Satea al-Haj said.
The chairman of Sudan's ruling military council, General Abdel Fattah al-Burhan, condemned the killings.
"What happened in Al-Obeid is sad. Killing peaceful civilians is an unacceptable crime that needs immediate accountability," the chairman of Sudan's ruling military council told journalists, according to state television.
The UN children's agency UNICEF called on the authorities "to investigate and hold all perpetrators of violence against children accountable".
"No child should be buried in their school uniform," it said in a statement, saying the students killed were between 15 and 17 years old.
Authorities announced a night-time curfew in four towns in North Kordofan state following the deaths in Al-Obeid, as the main protest group, the Sudanese Professionals Association, called for nationwide rallies against the "massacre".
All schools in the state have been told to suspend classes.
Thousands of Sudanese students took to the streets in the capital and elsewhere in the country to condemn the violence.
Videos posted online show thousands in school uniforms, schoolbags on their backs, marching Tuesday in the streets of Khartoum and in other places, denouncing the deaths.
"The Janjaweed forces and some snipers, without any mercy, confronted school students with live ammunition," the SPA said, referring to the RSF.
The SPA said more than 60 people have been wounded.
"The dead are children and that adds to the brutality of this cowardly incident," said a protest leader, Ismail al-Taj at a rally in Khartoum, as hundreds protested in the capital and its twin city of Omdurman on Monday.
Doctors linked to the protest movement say that more than 250 people have been killed in protest-related violence since December when demonstrations first erupted against now ousted president Omar al-Bashir.
Residents of Al-Obeid said the schoolchildren's rally had been over shortages of bread and fuel in the town.
It was a sudden tripling of bread prices that was the spark for the mushrooming protests that brought an end to Bashir's three decades of iron-fisted rule.
The power-sharing deal agreed on July 17 provided for the establishment of a new governing body of six civilians and five generals.
But the publication on Saturday of the findings of an investigation commissioned by the military into the deadly dispersal of a Khartoum protest camp has triggered angry demonstrations.
Shortly before dawn on June 3, gunmen in military fatigues raided the site of the weeks-long sit-in outside army headquarters, shooting and beating protesters.
Doctors linked to the protest movement say the raid left 127 people dead and scores wounded.
