Thousands of protesters chanting "revolution is the people's choice" took to the streets Tuesday in a city southeast of Sudan's capital to call on longtime leader Omar al-Bashir to step down. It's the latest in nearly three weeks of anti-government demonstrations.

The demonstration in Gadaref came just hours after Sudan's Interior Minister, Ahmed Bilal Othman, told Parliament that police have arrested 816 people since protests began in mid-December.

The demonstrations initially erupted over economic issues: high prices for, in particular, bread and medicines, as well as other staples, according Alexander Kliment, Eurasia Group's director of global research and a senior editor at GZero media.

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The protests have grown to reflect a much broader sense of frustration with the government and shifted to calls for Bashir to step down. He's been in power since he led a military coup in 1989. People taking to the streets are frustrated with economic mismanagement, corruption and political repression, Kliment said.

The protesters in Gadaref on Tuesday wanted to reach the provincial legislature to deliver a note demanding his departure. Police used tear gas and fired in the air to disperse them.

Othman said 19 people have been killed in the ongoing protests, including two members of the security forces, although Human Rights Watch said the death toll is about twice as high. An estimated 40 people, including children, have been killed since the protests started, the organization reported, citing medical workers and Sudanese activists.

Human Rights Watch said security forces have used live ammunition "and other forms of excessive force" against protesters, and that some have been arbitrarily detained.

"Sudanese have the right to protest peacefully and express their views without risking life or limb or getting locked up," Jehanne Henry, the organization's associate Africa director, said Tuesday.

Sudanese demonstrators chant slogans as they march along the street during anti-government protests in Khartoum, Sudan, December 25, 2018. Mohamed Nureldin Abdallah/REUTERS

Authorities have arrested scores of opposition leaders and imposed nighttime curfews and emergency laws in a number of cities across Sudan. They also suspended classes across most of the country.

Sudan's Parliament is packed with Bashir's loyalists, who are campaigning to amend the constitution to allow the general-turned-president, who is already one of the longest serving leaders in the region, to run for a new term in 2020 elections.

He has stayed in power for nearly three decades through "incredibly ruthless repression," by stoking and amplifying divisions within the country, and through a "pragmatic relationship" with outside powers, Kliment said.