CAIRO - Thousands of Sudanese students joined protests across the country Tuesday condemning the violent dispersal of a demonstration the day before that left six people dead.

The killings reignited tensions between the pro-democracy movement whose protests that toppled President Omar al-Bashir in April and the military council that has ruled since then. The two sides had been set to hold talks Tuesday to finalize a power-sharing agreement, but those were postponed after the deaths.

Security forces opened fire on a demonstration by teenage students in the city of Obeid on Monday. At least six people were killed, including four students, said the Sudanese Doctors Central Committee, which is the medical arm of one of the groups behind the protests.

Protest leaders said the deaths were caused by security forces, while local authorities said they had begun an investigation. The military condemned the violence.

Tuesday's marches were called by the Sudanese Professionals Association, which spearheaded the uprising that began in December and eventually toppled al-Bashir. The umbrella group is part of a larger coalition, the Forces for the Declaration of Freedom and Change, which is negotiating with the military over a transition to civilian rule.

Videos posted online showed thousands of students in school uniforms, with schoolbags on their backs, marching Tuesday in the streets of Khartoum and other places. One video showed students in the capital waving Sudanese flags and chanting slogans such as: "Free revolutionaries, we will continue our way forward."

Authorities cancelled school nationwide starting Wednesday and until "further notice," the state-run SUNA news agency reported. Officials in North Kordofan, where Monday's shootings took place, suspended classes shortly after the violence and imposed a nightly curfew in parts of the province.

The protest coalition and the military council had been set to meet Tuesday, but protest leader Nour al-Din Salah said his side pushed the meeting to Wednesday following the latest violence.

"A delegation from the Forces for the Declaration of Freedom and Change has travelled to the city of Obeid. ... The delegation includes the main negotiators," Salah said.

Both sides agreed on the outline of a power-sharing deal earlier this month but remain divided on a number of key issues, including whether military commanders should be immune from prosecution for violence against protesters.

Last month, security forces violently dispersed the protesters' main sit-in outside the military headquarters in Khartoum, killing dozens of people and plunging the fragile transition into crisis. The two sides returned to talks later that month after intense pressure from the United States and its Arab allies.

News from © The Associated Press, 2019