Sudanese police have fired tear gas to disperse hundreds of protesters outside a mosque belonging to an opposition party in the capital Khartoum, a witness has said.
The witness said on Friday that demonstrators carried Sudanese flags and banners reading "The people want the regime to fall", a slogan used by protesters during the Arab Spring uprisings over the past year.
The protesters had gathered in the capital's Hijra Square beside the mosque of the opposition Umma party. After the tear gas and an unknown number of arrests, demonstrators burned tyres and threw stones at police before running for cover, the witness told the AFP news agency.
"Police have fired tear gas at protesters as they attepmted to take to the streets following Friday prayers. There is a lot of defiance here, protesters have blocked the roads and they are burning tyres," said Al Jazeera's Zeina Khodr, reporting from Khartoum.
"People have been chanting 'We want the downfall of the government', so people here belive that this is the start of their revolution," she added.
Waffa al-Amin, an activist, told Al Jazeera by phone from the protests that "about 2,000" protesters had gathered in the Ummdurman district of the capital.
"We are surrpounded by 500 police and security forces. We have blocked the area so they can't get to us, however, they have been firing tear gas at us," al-Amin said.
Demonstrators planned major protests for Friday and Saturday, the 23rd anniversary of a coup by President Omar al-Bashir.
Some have called have dubbed this Friday "Licking the elbow" a phrase used Sudanese, and adopted by the government, to mean attempting the impossible.
The UN human rights chief has urged the Sudanese government to avoid "heavy-handed suppression".
"Tear gas, rubber bullets, live ammunition and other heavy-handed suppression will not resolve the frustrations and grievances of the people, said Navi Pillay, UN high commissioner for human rights, in a statement on Thursday.
Rights groups say scores of people have been arrested since protests against inflation began on June 16 in Khartoum.
Human Rights Watch said the government was also using the protests "to silence dissenters".
After Bashir announced austerity measures, including tax hikes and an end to cheap fuel, the protests spread to include a cross-section of people in numerous locations throughout the capital and other parts of Sudan.
Bashir, suggesting that someone was behind the disturbances, has called them small-scale and not comparable to the Arab Spring uprisings in Egypt and elsewhere. He maintains that he remains popular.
Sudan has lost billions of dollars in oil receipts since South Sudan gained independence last July, taking with it about 75 per cent of Sudanese crude production.
For more than a week, demonstrators in groups of 100 or 200 have burned tyres, thrown stones and blocked roads, while calling for a change in government.
"After 23 years of endurance, the Sudanese people have decided to say enough is enough," said an activist from the movement Sudan Change Now.
Protests by tens of thousands in 1964 and 1985 helped bring about the downfall of the Sudanese regimes then in office.
Bashir is a former army officer who seized power in 1989.