Sudan's army rulers and protest leaders on Sunday inked a hard-won constitutional declaration, paving the way for a promised transition to civilian rule.

Four protesters were shot dead at a rally in the Sudanese city of Omdurman on Thursday, medics said, as protest leaders and ruling generals started talks to thrash out remaining issues on transitioning to civilian rule.

A top Sudanese general has said the six protesters including four school children killed at a rally this week were shot dead by members of a feared paramilitary force.

Sudanese authorities Tuesday ordered all schools nationwide to suspend classes indefinitely after crowds of students launched demonstrations against the killing of six protesters including five pupils at a rally in a central town.

Negotiators for Sudan's protest movement said Tuesday they would not be holding planned talks with the country's ruling generals as they were visiting a town where five teenaged protesters were killed.

The United Nations called for a probe into the killing of five schoolchildren at a Sudan rally as protesters piled on pressure on army rulers to transfer power ahead of talks on the country's transition Tuesday.

Protesters accused the feared paramilitaries of the Rapid Support Forces, headed by powerful General Mohamed Hamdan Daglo, of shooting dead the five teenagers at a rally held against shortages of bread and fuel in the city of Al-Obeid on Monday.

Sudanese protest leaders told AFP Friday talks with the country's army rulers have been postponed, just days after the two sides signed a power sharing deal.

Just days after protest leaders and Sudan's ruling generals agreed a power sharing deal, they are set to meet again on Friday for talks on key remaining issues.

The two sides inked an accord Wednesday to form a joint ruling body tasked with creating a transitional civilian administration that would govern for just over three years -- a key demand of protesters.

Sales have tumbled at Hashem Abul Fadel's shopping centres in Sudan, where he and fellow business owners fear that months of political turmoil could bring on a full-scale economic collapse.

Sudan's protesters and ruling generals Wednesday inked a power sharing deal that aims to install a civilian administration, a key demand of demonstrators since president Omar al-Bashir was deposed three months ago.