Khartoum:
Rights groups slammed Sudan for killing protesters demonstrating against fuel subsidy cuts, saying 50 people were shot dead in two days in the country's worst riots since 1989.
Activists called for the protests to continue and urged the security forces to side with the people.
The African Centre for Justice and Peace Studies and London-based Amnesty International said 50 people were killed after being shot in the head or chest on Tuesday and Wednesday.
"Local sources and activists have put the figure much higher, in excess of 100," the groups said in a joint statement.
They also expressed "deep concern" about reports of hundreds being detained and urged the authorities "to ensure that they are protected from torture and other ill-treatment".
"Shooting to kill - including by aiming at protesters' chests and heads - is a blatant violation of the right to life, and Sudan must immediately end this violent repression by its security forces," said Lucy Freeman, Africa Deputy Director at Amnesty.
Reports from Khartoum on Thursday said at least 29 people were killed since rioting erupted on Monday in the largest protests since President Omar al-Bashir seized power in 1989.
Police confirmed the 29 fatalities without giving details, but hospital and other sources said most had been shot dead.
"At least 50 people have been killed and 100 injured since the protests began, according to sources interviewed by the organisations," the rights groups said.
The statement said the dead included a 14-year-old Khartoum boy.
Osman Hummaida, Executive Director of the African Centre for Justice and Peace Studies, called on Sudan to investigate "the use of disproportionate force and allegations of the intentional killing of protesters and use of live ammunition by security forces".
Activists have called for further protests today.
Protests first erupted on Monday in Wad Madani in Gezira state south of Khartoum, the scene of the first death, and later spread to Nyala, the capital of South Darfur state.
A hospital source in Khartoum's twin city Omdurman told AFP on Thursday that "we have received the bodies of 21 people" since the protests began, adding that all were "civilians".
Another eight people were killed in other regions, witnesses and families said.
Late on Thursday, police fired tear gas to disperse hundreds of demonstrators in Omdurman, and a small protest was also held in the capital itself.
"The people want the fall of the regime," protesters, many of them students, chanted in Khartoum on Wednesday, echoing the refrain of Arab Spring protests that toppled several governments in 2011.
The education authorities have announced the closure of schools until next Monday.
Young activists called on demonstrators to keep up "the revolution and their protests" until the fall of the regime, urging the security forces to side with the people.
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".
The American embassy has urged its citizens to avoid flashpoint areas, warning of the danger of further protests.
Petrol and diesel prices at the pump shot up when fuel subsidies were scrapped after Bashir said they had reached "a level that is dangerous for the economy".
Inflation is already running at 40 percent.
Khartoum lost billions of dollars in oil receipts when South Sudan gained independence two years ago, taking with it about 75 percent of the formerly united country's crude production.
Since then, Sudan has been plagued by a weakened currency and a severe shortage of dollars to pay for imports.
As the protests swept the country, the foreign ministry denied Bashir has cancelled a trip to address the UN General Assembly.
It urged the US government "to respect its obligations and issue visas to President Omar al-Bashir and the delegation accompanying him to New York."
The International Criminal Court has urged the United States to arrest Bashir who is wanted by the court in The Hague on 10 counts of war crimes, crimes against humanity and genocide in Sudan's Darfur conflict.