Sudanese police fired tear gas Thursday to disperse anti-government protesters marching to the presidential palace in the capital, activists said, the latest in two months of street protests seeking autocrat President Omar al-Bashir's ouster.
The protests erupted in December, initially over surging prices and a failing economy, but quickly turned into calls for al-Bashir's resignation after nearly 30 years in power.
Thursday's march was called for by an umbrella of independent professional unions, backed by opposition parties. Thousands gathered in the United Nations square before heading to the presidential palace on in central Khartoum.
Online video footage shows protesters chanting, "Freedom, peace, justice and the revolution is people's choice."
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Police descended on the protesters with tear gas and batons, not allowing them to reach the palace as in previous marches. There were no immediate reports of casualties.
Elsewhere, hundreds of demonstrators gathered in the Zamzam refugee camp the country's troubled Darfur region on Thursday, shouting against al-Bashir's rule.
On Wednesday, Sudan's main opposition groups held in a joint press conference in Khartoum's twin city of Omdurman, their first since the wave of unrest, calling for a four-year transitional government followed by elections.
"We have decided on a program that would take place after the fall of the regime, and (we will) hold a constitutional dialogue conference at the end of the transitional period to decide how Sudan will be ruled," said Mohamed Mokhtar al-Khatib, a senior leader of the Communist Party.
Sudanese police have used tear gas, rubber bullets, live ammunition and batons to quell the unrest. They have imposed emergency laws and night-time curfews in some cities, and have suspended classes in schools and universities in others. They have arrested opposition leaders, doctors, journalists, lawyers and students along with some 800 protesters.
The country's intelligence and security officials, along with al-Bashir, insist that the rallies are the work of what they describe as "evil" foreign powers, and have vowed to stop them.
Last month, authorities ordered the release of all protesters who were detained since Dec. 19. But Human Rights Watch said only 186 were reported released and that video evidence showed signs of torture on released detainees.
Activists say at least 57 people have been killed in the protests. The government's latest tally stands at 30 killed, but figures have not been updated in days.
Al-Bashir, who seized power in an Islamist-backed military coup in 1989, insists that only elections, which he intends to take part in, will result in change. Wanted for genocide by the International Criminal Court over the fighting in Darfur, he has repeatedly warned that the protests could plunge Sudan into the kind of chaos convulsing other countries in the region.