Four Sudanese school students were among five demonstrators shot dead on Monday during a rally against shortages of bread and fuel, a day before protest leaders and ruling generals are set to hold new talks on the country's transition.

Authorities announced a night-time curfew in four towns following the deaths in the central town of Al-Obeid, as a key protest group called for nationwide rallies against the "massacre."

The ruling military council and protest leaders earlier this month inked a power-sharing deal providing for a joint civilian-military administration which in turn would install civilian rule.

That is the main demand of a nationwide protest movement that led to the April ouster of longtime leader Omar al-Bashir and has since demanded that the generals who took his place cede power to civilians.

But on the eve of Tuesday's talks aimed at resolving outstanding issues over the transition, five protesters were killed in Al-Obeid, the capital of North Kordofan state, said a doctors' committee linked to the protest movement.

"Five martyrs succumbed to direct wounds from sniper bullets during a peaceful rally in Al-Obeid," the committee said in a statement.

Prominent protest leader Babikir Faisal told AFP that the dead included "four high school students."

Monday's deaths sparked calls for talks set for Tuesday to be suspended.

"We cannot sit at the negotiating table with those allowing the killing of revolutionaries," Siddig Youssef, a prominent protest leader, said in a statement.

Tuesday's talks were set to cover issues including the powers of the joint civilian-military ruling body, the deployment of security forces and immunity for generals over protest-related violence, according to protest leaders.

The power-sharing deal agreed on July 17 provided for the establishment of a new governing body of six civilians and five generals.

It was then to oversee the formation of a transitional civilian government and parliament to govern for 39 months, followed by elections.

Khartoum has seen angry demonstrations since Saturday, when investigators announced the results of a probe showing into a deadly crackdown on a protest camp.

Shortly before dawn on June 3, gunmen in military fatigues raided the site of a weeks-long sit-in outside the military headquarters in Khartoum, shooting and beating protesters.

Doctors linked to the protest movement say the raid left 127 people dead and scores wounded.

But the joint investigation by prosecutors and the ruling military council that took power following Bashir's ouster found that just 17 people were killed on June 3, with a total of 87 dying between that day and June 10.

The probe identified eight officers involved in the violent crackdown on the protest camp, including three from the feared Rapid Support Forces paramilitary group.

But protest leaders have rejected the findings, saying the inquiry exonerated the military council and gave a far lower death toll than their own figures.

The country’s ruling generals have insisted they did not order the dispersal of the sit-in.