Police in Sudan have used tear gas to break up a student protest at the University of Khartoum in the latest crackdown on public dissent against President Omar al-Bashir.
About 1,000 students chanting: "The people want the downfall of the regime" and "Down, down with military rule" tried to force their way out of their campus, but were driven back inside by police who fired volleys of tear gas at them, witnesses said.
Some 150 students temporarily broke through the cordon after throwing stones at police, before also being driven back inside, a student and an activist told the Reuters news agency.
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The police were not immediately available to comment.
Zeina Khodr, Al Jazeera's correspondent in Khartoum, said: "Students tried to force their way out of the university campus, the police drove them back, they used tear gas and students threw stones at the police vehicles but eventually they were forces to retreat inside the campus.
"There was also a confrontation between students that are supporting the government, and those who are opposing the government.
"There are reports of injuries but I can't confirm it."
Sudan has so far avoided the sort of mass unrest that overthrew rulers in Egypt and Tunisia last year, but small anti-government demonstrations have broken out over the last three weeks, driven by rising anger over austerity measures and Bashir's 23 years in power.
Authorities have so far swiftly put the protests down, using batons and teargas.
On Friday, security forces also fired tear gas at worshippers trying to leave a mosque to demonstrate after prayers, witnesses said.
The University of Khartoum has symbolic significance in Sudan's political history as it was the centre of popular uprisings in 1964 and 1985, both of which ousted military rulers.
On Saturday night, security agents arrived at the house of Kamal Omar, a prominent member of the opposition Popular Congress Party, at around 11:00 pm [20:00 GMT] and arrested him, his wife said.
"Two cars came to our house and about five security officers came inside," she told Reuters.
Another party leader confirmed the arrest. There was no immediate comment from the security services.
The arrest followed a declaration on Wednesday signed by the country's main opposition parties that backed the demonstrations, even though they have not yet brought their supporters onto the streets in large numbers.
Omar's party is headed by Hassan al-Turabi, once one of Sudan's most influential politicians and a former spiritual mentor to Bashir, who came to power in a bloodless 1989 coup.
Turabi himself has been arrested a number of times.
The two men fell out in the late 1990s and Turabi has since become one of the government's most outspoken critics.
Sudan has been battling an economic crisis - including a budget deficit, high inflation and a depreciating currency - since South Sudan took three-quarters of the country's oil production with it when it seceded a year ago.
Oil was previously Sudan's main source of revenues and foreign currency.
Last month, the government announced tough austerity measures aimed at stabilising the economy, a move which triggered a spate of small demonstrations, that began on university campuses before spreading beyond the capital.
The protests have rarely gathered more than a few hundred people at any one time, but are an added challenge for a government which is already trying to quell multiple armed rebellions.
Source: Al Jazeera and agencies