Fresh deadly protests have broken out in Sudan, taking the toll of people killed in three days of rioting to 29.
Police fired tear gas to disperse hundreds of demonstrators late on Thursday in Khartoum's twin city of Omdurman, and a small protest was also held in the capital itself.
The demonstrations have been prompted by a government decision to cancel fuel subsidies.
Calm was restored in Khartoum earlier on Thursday after anti-riot units were deployed at major road intersections, but activists called on social media for fresh protests on Friday.
The escalating protests are the largest in Sudan since President Omar al-Bashir, whose Foreign Ministry denied he had called off a visit to the UN, seized power in 1989.
Protests called for by activists took off from Inqaz district, south of Khartoum, where up to 3,000 people marched on the main road and hurled stones at passing-by cars, witnesses said.
Police responded by firing tear gas and rubber bullets, they said. No casualties were reported.
A hospital source in Omdurman told AFP news agency that "we have received the bodies of 21 people" since the protests began on Monday, adding that all were "civilians".
Another eight people were killed in other regions, witnesses and families said.
Police confirmed the 29 fatalities without giving details on the killings, but the sources said most of them were shot dead by security forces.
Riots erupted in several districts of Khartoum on Wednesday, some near the city centre, and public transport ground to a halt.
"Freedom, freedom," and "The people want the fall of the regime," chanted the protesters, many of them students, borrowing the refrain of Arab Spring protests that toppled several governments in 2011.
The protests have turned violent in some areas, with government buildings set ablaze.
Demonstrations first erupted in Wad Madani in Gezira state, south of Khartoum, the scene of the first death on Monday.
They have also spread to Nyala, capital of South Darfur state.
The education authorities have announced the closure of schools until next Monday.
The Internet was restored on Thursday, users said, after a one-day cut for unexplained reasons.
Social media was filled with calls for fresh protests on Friday after the weekly Muslim prayers.
The Alliance of the Youth of the Sudanese Revolution, in a statement, said its aims were for Bashir to step down "along with the corrupt government and for its services to be dismantled".
In a related development, the US embassy has called on its citizens to avoid flashpoint areas, saying it had received "regrettable" reports of casualties and warning Americans of the danger of further protests.
Bashir had been scheduled to speak to world leaders on Thursday, but Jerome Bernard, a UN spokesman, told AFP that Ali Karti, Sudanese foreign minister, would now address the assembly instead.
The Foreign Ministry denied the report and urged the US to "respect its obligations and issue visas" to Bashir and his delegation, and to stop delaying the applications.
The International Criminal Court has urged US authorities to arrest Bashir, who is wanted by the court in The Hague on 10 counts of war crimes, crimes against humanity and genocide in the Darfur conflict.
The ICC issued arrest warrants for Bashir in March 2009 and July 2010, but he has since travelled to several African countries.