Sudanese police fired teargas and used batons on Sunday to break up a demonstration of opposition party members over the detention of several activists and politicians, witnesses said.
About 40 members of the African country's main opposition parties had gathered in front of the house of Sudan's first post-independence president in the Omdurman area of Khartoum, giving speeches and chanting.
"The people want to overthrow the regime," they chanted, and, "Freedom, freedom."
Police fired teargas at the protesters and used batons to disperse them, the witnesses said. There was no immediate comment from the police.
Small protests have broken out in Sudan over rising food prices and cuts to government fuel subsidies over the last two years, but the country has avoided the sort of mass unrest that unseated rulers in neighbouring Egypt and Libya.
The protesters, who included members of the Umma, Popular Congress and Communist parties, were protesting against the detention of activists and politicians who had attended a meeting with armed rebel groups in Uganda early this year.
The secession of oil-producing South Sudan in July 2011 stoked high inflation after a loss of foreign currency led to a depreciation in the Sudanese pound and made it more expensive to import food and fuel.