Sudanese security forces fired tear gas to disperse thousands of protesters, some burning car tyres, who gathered to mark the anniversary on Monday of a transitional power-sharing deal with demands for quicker political reform.

The agreement set up a precarious alliance of civilian technocrats and military officials following the April 2019 ouster of long-time ruler Omar al-Bashir, with elections due to be held after 39 months.

The government says it is pushing ahead with reforms, but many people want swifter and deeper change.

Protesters from neighbourhood-based "resistance committees" gathered outside Cabinet headquarters in downtown Khartoum to voice their demands amid a heavy security presence.

The Sudanese Professionals Association (SPA), which spearheaded anti-Bashir protests and helped strike the deal with the military, said on Twitter that security forces violently dispersed protesters after they demanded to meet Prime Minister Abdallah Hamdok and refused an envoy sent in his place.

A Reuters witness saw tear gas being fired.

The police said in a statement late on Monday that officers' use of tear gas during the demonstration was lawful and according to their evaluation of the situation on the ground but has lead to "some random injuries" among protesters and security forces.

Khartoum's governor Ayman Khalid expressed his "deepest apologies" and called the force used on Monday "excessive" and "contradictory to [our approach] in the era of freedom, peace and justice."

Khalid also called on the general prosecutor to investigate.

The neighbourhood committees say they want to see the long-delayed formation of a transitional legislature, the reorganisation of the civilian Forces of Freedom and Change coalition and a civilian takeover of military-run companies.

Hamdok on Monday called for political and popular support for reform.

"The state apparatus needs to be rebuilt, the legacy of (the old regime) needs to be dismantled and the civil service needs to be modernized and developed to become unbiased between citizens, as well as effective," he said in a statement.