The fresh demonstrations come at a time when US diplomats are visiting Khartoum in a bid to bolster UN-led efforts to cajole the military into restoring a transition to full civilian rule.
Thousands of Sudanese have rallied to protest against the killings of dozens in a crackdown since last year's military coup, as US diplomats pressed for an end to the violence.
Protesters converged from several parts of the capital onto a main artery in east Khartoum on Thursday, according to an AFP correspondent.
"The military should go back to the barracks," protesters chanted at one rally.
Others gathered outside the United Nations headquarters in Khartoum with banners reading "no to external solutions".
They also called on the UN special representative to Sudan, Volker Perthes, "to leave".
In the capital's twin city of Omdurman, Sudanese security forces fired tear gas at the protesters, witnesses said.
The demonstrations were the latest since the October 25 coup led by General Abdel Fattah al Burhan, which derailed a civilian-military power-sharing deal painstakingly negotiated in the wake of the 2019 ouster of autocrat Omar al Bashir.
On Wednesday, US Assistant Secretary of State Molly Phee and special envoy for the Horn of Africa, David Satterfield, held meetings with the bereaved families of people killed during the protests.
At least 72 people have been killed — including many by live rounds — during the ongoing crackdown, according to a count by a pro-democracy group of medics.
The US officials "strongly condemned the use of disproportionate force against protesters, especially the use of live ammunition and sexual violence and the practice of arbitrary detention", Washington's embassy in Khartoum said in a statement on Thursday.
They also warned that the US "will not resume paused assistance to the Sudanese government absent an end to the violence and a restoration of a civilian-led government that reflects the will" of Sudan's citizens.
The US has suspended $700 million in assistance to Sudan since the coup, as part of wider international punitive measures.
Sudan's authorities have repeatedly denied using live ammunition against demonstrators, and insist scores of security personnel have been wounded during protests. A police general was stabbed to death a week ago.
Last week, Perthes launched consultations among Sudanese factions in a bid to resolve Sudan's ongoing political crisis .
The ruling Sovereign Council — formed by Burhan following the coup with himself as chairman — has welcomed the UN-led dialogue, as have the United States, Britain, the UAE, Saudi Arabia and Egypt.
The mainstream faction of the Forces for Freedom and Change — the main civilian faction — also joined consultations "to restore the democratic transition".