Detained Prime Minister Hamdok was reinstated after agreeing to partner with the military to "stop the bloodshed" but protest organisers have cried "treason".
Sudanese security forces have fired tear gas at thousands of protesters who rallied against a deal that saw the prime minister reinstated after his ouster in a military coup last month.
Demonstrators in the capital, Khartoum, chanted "the people want the downfall of the regime" on Thursday while in the capital's twin city Omdurman others shouted "power to the people, a civilian government is the people's choice".
Security forces fired tear gas to disperse protesters in Omdurman as well as in the central state of North Kordofan and in North Darfur, witnesses said.
Thursday's rallies displayed the rebuff over an agreement that saw General Abdel Fattah al Burhan reinstate Abdalla Hamdok as prime minister.
In Khartoum, demonstrators chanted "the people want the downfall of the regime" while protesters in North Khartoum reserved their ire for the general, chanting "Burhan is dirty".
Volker Perthes, the UN special envoy to Sudan who helped mediate between the military and civilian factions after the coup, said Wednesday that the rallies were "another test of credibility" of the agreement.
He urged authorities to allow demonstrations to go ahead "without bloodshed or arbitrary arrests".
Earlier, activists took to social media to call for "Martyrs' Day" demonstrations on Thursday, in honour of the 42 protesters killed in the post-coup crackdown, according to an updated toll from medics.
Backlash over agreement
The detained Hamdok, who has been prime minister in the transitional government since the ouster of long-time autocratic ruler Omar al Bashir in 2019, said Wednesday he had partnered with the military in order to "stop the bloodshed" and to "not squander the gains of the last two years".
The deal he signed with Burhan lays down a "clear date" for Sudan's first free elections in three decades slated for July 2023, the premier said.
But protest organisers in the northeast African state have accused Hamdok of "treason" and vowed to maintain pressure on the military-civilian authority.
Twelve out of 17 ministers from a bloc calling for a purely civilian government, on the other hand, resigned on Monday, rejecting Hamdok's strategy of engaging with the military.
Burhan seized power and detained Hamdok on October 25, but after international condemnation and mass protests he reinstated the premier on Sunday.