Sudanese security forces deployed on Khartoum's streets Thursday, sealing the capital off from its suburbs and cutting mobile internet as opponents of the military government prepared to hold fresh protests.

Pro-democracy activists have kept up a campaign of street demonstrations against the army's October 25 coup despite a crackdown that has seen at least 48 people die in protest-related violence, according to the independent Doctors' Committee.

Army, police and paramilitary patrols criss-crossed Khartoum's streets, while shipping containers blocked the Nile bridges that connect the capital with its northern suburbs and its twin city Omdurman.

The bridges were blocked off for the last protests on December 26, when tens of thousands took to the streets.

But for Thursday's planned protests, new surveillance cameras had been installed on the major thoroughfares along which demonstrators were due to march.

Activists use the internet for organising demonstrations and broadcasting live footage of the rallies.

- US appeal for calm -

The US embassy appealed for restraint from the government led by military chief General Abdel Fattah al-Burhan, which had been counting on a controversial November partnership deal with civilian Prime Minister Abdalla Hamdok to calm public anger.

"The US embassy reiterates its support for peaceful expression of democratic aspiration, and the need to respect and protect individuals exercising free speech," a statement said.

"We call for extreme discretion in use of force and urge authorities to refrain from employing arbitrary detention."

Activists have condemned sexual attacks during December 19 protests, in which the UN said at least 13 women and girls were raped.

Hamdok had been held under effective house arrest for weeks before being reinstated under the November deal, which promised elections for July 2023.

But the deal was widely criticised as a gift to the military that gave a cloak of legitimacy to its coup.

Sudan still has no functioning government, a prerequisite for the resumption of international aid cut in response to the coup.

Over 14 million people, a third of Sudan's population, will need humanitarian aid next year, according to the UN Office for the Coordination of Humanitarian Affairs, the highest level for a decade.