Unidentified armed men arrested a number of Sudanese leaders early Monday, a government source told AFP, after weeks of tensions between the military and civilian transitional authorities.
The internet was cut across the country, AFP journalists said, as demonstrators gathered on the streets to protest the arrests, setting fire to tyres.
Men in military uniform cut off the main roads leading to the capital, and state television was broadcasting patriotic songs.
The news comes just two days after a Sudan faction calling for a transfer of power to civilian rule warned of a "creeping coup", during a press conference that an unidentified mob attack had sought to prevent.
Sudan has been undergoing a precarious transition marred by political divisions and power struggles since the April 2019 ouster of president Omar al-Bashir.
Since August 2019, the country has been led by a civilian-military administration tasked with overseeing the transition to full civilian rule.
The main civilian bloc -- the Forces for Freedom and Change (FFC) -- which led the anti-Bashir protests in 2019, has splintered into two opposing factions.
"The crisis at hand is engineered -- and is in the shape of a creeping coup," mainstream FFC leader Yasser Arman told the Saturday press conference in the capital Khartoum.
"We renew our confidence in the government, Prime Minister Abdalla Hamdok, and reforming transitional institutions -- but without dictations or imposition," Arman added.
Tensions between the two sides have long simmered, but divisions ratcheted up after a failed coup on September 21 this year.
Last week tens of thousands of Sudanese marched in several cities to back the full transfer of power to civilians, and to counter a rival days-long sit-in outside the presidential palace in the capital Khartoum demanding a return to "military rule".
Hamdok has previously described the splits in the transitional government as the "worst and most dangerous crisis" facing the transition.
On Saturday, Hamdok denied rumours he had agreed to a cabinet reshuffle, calling them "not accurate".
The premier also "emphasised that he does not monopolise the right to decide the fate of transitional institutions."
Also on Saturday, US Special Envoy for the Horn of Africa Jeffrey Feltman met jointly with Hamdok, the chairman of Sudan's ruling body General Abdel Fattah al-Burhan, and paramilitary commander Mohamed Hamdan Daglo.
"Feltman emphasised US support for a civilian democratic transition in accordance with the expressed wishes of Sudan's people," the US embassy in Khartoum said.
Analysts have said the recent mass protests showed strong support for a civilian-led democracy, but warned street demonstrations may have little impact on the powerful factions pushing a return to military rule.
