Crowds of Sudanese protesters on Sunday held rallies in their neighborhoods and some squares in the capital and its twin city of Omdurman after organizers called for more anti-government demonstrations.
Protests sparked by a government decision to raise the price of bread have rocked the east African country for weeks.
The demonstrations have mushroomed into nationwide rallies against the government of President Omar al-Bashir, who swept to power in 1989 in an Islamist-backed coup.
Officials say 30 people have died in the violence since the protests first erupted on December 19 in the farming town of Atbara before spreading to Khartoum and other regions.
Rights groups say more than 40 people have been killed.
On Sunday, protesters came onto the streets in Khartoum and Omdurman to hold sit-ins in several squares, responding to a call by the Sudanese Professionals Association which is leading the protest campaign.
But a massive deployment of riot police and security agents prevented them from gathering at several locations, witnesses said, after which the protesters began rallies in three residential areas of Khartoum and two in Omdurman, across the Nile.