Sudanese police fired tear gas on Tuesday at crowds of people chanting "Peace, justice, freedom" in the capital, witnesses said, after organisers of anti-government demonstrations called for new protests.
Men and women had gathered in Khartoum's southern business district of El-Kalakla, the witnesses said, but they were quickly confronted by riot police with tear gas.
Protesters chanted "Peace, freedom, justice" and "We are fighters, we will achieve our mission," a witness told AFP.
Demonstrators carrying the Sudanese flag and banners declaring "Revolution is the people's choice" marched in the district as riot police moved in to disperse them.
As darkness fell, the protesters broke up into groups and staged small rallies in streets and alleys as police chased them, witnesses said.
The Sudanese Professionals' Association that is spearheading the rallies has urged protesters to continue with their near daily demonstrations this week, calling it the "Week of Uprising".
Deadly protests have rocked Sudan since December 19 when angry people took to the streets in towns and villages against a government decision to raise the price of bread.
At least 24 people have died in the protests, which swiftly turned into nationwide rallies in which demonstrators called on President Omar al-Bashir to step down.
Ahead of Tuesday's demonstration, authorities had deployed police in the district and in some areas of Omdurman, across the Nile river, but reinforcements swiftly joined riot police after protesters came to the streets.
Rights groups say more than 1 000 people have been arrested since the protests began, including opposition leaders, activists and journalists as well as demonstrators.
Although the unrest was triggered by the rise in the price of bread, Sudan has faced a mounting economic crisis in the past year, including an acute shortage of foreign currency.
Repeated shortages of food and fuel have been reported across cities, while the cost of food and medicine has more than doubled.