Police have fired tear gas at hundreds who gathered in central Khartoum and outside the city's main university, protesting against the killing of a student at a campus demonstration a day earlier, witnesses say.
Crowds chanted: "Killing of a student, killing of a nation, down with military rule," at the rare rally in the centre of the heavily-guarded Sudanese capital on Thursday (local time).
Protesters later blocked a road and set fire to tyres outside Khartoum University.
Police fired tear gas canisters and used batons to beat protesters who hurled rocks back at them.
Students had initially demonstrated on Wednesday against government plans to sell off Khartoum University buildings, before witnesses said gunmen in plain clothes opened fire on them, killing 20-year-old Mohammed al Sadek.
Anti-government-protests erupted at his funeral later on Wednesday.
The government said on Thursday that unnamed armed groups were trying to undermine security at Sudan's universities -- long centres for political activism and debate.
"The government will not allow any disruption to the stability of universities," President Omar Hassan al-Bashir's aide, Ibrahim Mahmoud, told the Sudanese Media Centre, an agency which is close to Sudanese security services.
Bashir, who took power in a 1989 coup backed by the army and Islamists, brooks little dissent in Sudan, which has been suffering from an economic crisis since South Sudan seceded in 2011, costing Khartoum more than 70 percent of its oil revenues.
The former army officer is wanted by the Hague-based International Criminal Court on charges of masterminding genocide, crimes against humanity and war crimes during Sudan's Darfur conflict. He denies wrongdoing.
"I remain concerned about a number of human rights issues in the country," Aristide Nononsi, the United Nations Independent Expert on the Situation of Human Rights in the Sudan, said in a statement on Thursday.