Rights groups slammed Sudan on Friday for killing protesters demonstrating against fuel subsidy cuts, saying 50 people were shot dead in the country's worst riots since 1989.
Activists, meanwhile, called for the protests to carry on and urged the security forces to side with the people.
Trying to maintain a blackout on the trouble, the authorities seized or blocked publication of three newspapers, even though they are considered pro-government, journalists said.
Friday's Al-Sudani and Al-Majhar al-Siassi dailies were seized at the printing press, they said, while Al-Watan was ordered not to print after covering the unrest in its Thursday edition.
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," 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 24 years ago.
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.
Troops on the streets
Activists have called for further protests after the weekly Muslim prayers on Friday, and security forces were deployed near official buildings, including some troops.
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.
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, have chanted in Khartoum, echoing the refrain of Arab Spring protests that toppled several governments in 2011.
The education authorities have announced the closure of schools until 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 warned its citizens to avoid flashpoint areas because 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.
As the protests swept the country, the foreign ministry denied Bashir has cancelled a trip to address the UN General Assembly, originally planned for Thursday.
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 called on Washington to arrest Bashir who is wanted by the court in The Hague for alleged war crimes, crimes against humanity and genocide in Sudan's Darfur conflict.