Sudanese security forces have broke up demonstrations across Khartoum as days of protests against government spending cuts expanded beyond the base of student activists who have dominated them so far, witnesses said.

At least seven protests were reported across the capital after Friday prayers, including in several neighbourhoods that had been quiet, which marked a significant increase over previous days.

About 400 to 500 protesters began chanting "the people want to overthrow the regime" as they left the Imam Abdel Rahman mosque in the suburb of Omdurman, activists and two witnesses said.

As security forces gathered, the protesters called for the police to join them, chanting: "Oh police, oh police, how much is your salary and how much is a pound of sugar?"

The police fired tear gas and then used batons as they clashed with the protesters, who threw rocks. Witnesses said men in civilian clothes also attacked the demonstrators.

Police were not immediately available for comment.

Oil dispute

Sudan has faced soaring inflation since South Sudan seceded a year ago - taking with it about three quarters of the
country's oil production.

Activists have been trying to use public frustration to build a movement to topple the government of President Omar Hassan al-Bashir.

Large demonstrations have been relatively rare in Sudan, which has avoided the mass "Arab Spring" protest movements which swept through neighbouring Egypt and Libya. Security forces usually quickly disperse protests.

But government moves to cut spending to plug a budget gap, including scaling back fuel subsidies, sparked a spate of small demonstrations this week.

At another protest in Omdurman, about 100 people chanted "Freedom, freedom" until police fired tear gas to disperse them.

Police also fired tear gas to break up separate protests in two central Khartoum neighbourhoods that had not previously seen protests, witnesses said. The demonstrators burned tyres at one of the protests, a witness said.

Broad segment

Unlike previous days, when the demonstrations were led largely by students, the protesters on Friday appeared to
encompass a broader segment of the capital's population.

Two small protests also broke out in the northern suburb of Bahri, which police dispersed with batons, activists said. A witness confirmed the account.

A group of about 40 people joined one protest in Bahri, but stopped amid a heavy security presence, while about 100 people burned tyres at the other protest until the police broke them up.

Sudan was supposed to continue collecting some revenues from South Sudan's oil because the landlocked new nation has to export its crude through the north.

But the two failed to set a price, and South Sudan shut down its production in January after Khartoum started confiscating some oil.

African Union-brokered talks in Addis Ababa have so far failed to yield a settlement.