Sudanese riot police fired tear gas at demonstrators in the capital Khartoum on Monday, dispersing protesters who had planned to march on the presidential palace following deadly anti-government rallies.
Crowds of men and women chanting "freedom, peace and justice" and "revolution is the people's choice" gathered in downtown Khartoum, but they were quickly confronted by police, witnesses told AFP.
Demonstrators gathered in groups in and around the downtown area, but were unable to converge to march towards the palace of President Omar al-Bashir.
As police fired tear gas, protesters were seen taking refuge in small lanes of the capital's usually busy business district that was deserted on Monday.
Most shops and businesses in downtown Khartoum were shut ahead of the planned march.
Monday's march was called by a group of professionals including doctors, teachers and engineers, which organised a similar rally on December 25.
"We will march towards the presidential palace calling for President Omar al-Bashir to step down," the Sudanese Professionals' Association said in a statement late on Sunday.
Opposition groups and prominent rebel chief Abdel Wahid al-Nur from war-torn Darfur had also urged their supporters to participate in the demonstration.
Hundreds of police officers and security forces deployed to key squares across the capital in the early morning to prevent the march.
Bashir has told police to abstain from using excessive force against the demonstrators after 19 people, including two security personnel, were killed in clashes in the initial days of demonstrations that erupted on December 19.
Rights group Amnesty International says 37 people have been killed in protests so far.