The demonstrations are to take place nearly three weeks after top general Abdel Fattah al-Burhan ousted the government, detained the civilian leadership and ordered a state of emergency.
The military's October 25 takeover drew widespread international condemnation and sparked street demonstrations by people demanding it restore the country's democratic transition.
Any hopes they had that the military would back down were dashed on Thursday, however, when Burhan named himself as the head of a new ruling Sovereign Council, triggering more condemnation from the West.
Ahead of the new demonstrations expected on Saturday, the military, police and paramilitary forces deployed in large numbers in Khartoum and sealed off bridges connecting the capital to neighbouring cities, AFP correspondents reported.
They also blocked roads leading to the army headquarters in Khartoum, the site of a mass sit-in protest in 2019 that led to the ouster of autocratic president Omar al-Bashir, said the correspondents.
The United Nations called on Sudanese security forces to refrain from violence ahead of Saturday's protests.
"In light of tomorrow's demonstrations in #Sudan I once again call upon the security forces to exercise utmost restraint and respect the right to peaceful assembly and freedom of expression," said UN Special Representative for Sudan Volker Perthes.
Saturday's planned demonstrations have largely been organised by informal groups known as "resistance committees" in neighbourhoods and towns across the country which emerged during the anti-Bashir demonstrations in 2019.
The committees have called for multiple protests since the coup and mobilised crowds via text messages as Sudan has largely remained under a rigorous internet outage with phone lines intermittently disrupted.
But despite the efforts, "civilian opposition to the coup has been diffuse and fragmented", Jonas Horner of the International Crisis Group said in a report last week.
A crackdown on demonstrations so far has left dead at least 15 people, according to an independent union of medics, leading to punitive measures by the international community.
'Gravely concerned'
On Friday, military figures and new civilian members of the new ruling council were sworn in before Burhan following its formation the day before.
Three former rebel leaders who were members of the ousted Sovereign Council and were appointed in the new one but did not attend the ceremony. They had previously rejected the military coup.
The newly named council features several new and little-known figures to represent civilians.
But it excludes any members of the Forces for Freedom and Change (FFC), an umbrella alliance which spearheaded the 2019 anti-Bashir protests, and the main bloc calling for a transition to civilian rule.
The UN has criticised the military's latest "unilateral" step, while Western countries said it "complicates efforts to put Sudan's democratic transition back on track".
"The Troika (Norway, the United Kingdom, the United States), the European Union, and Switzerland are gravely concerned by the purported appointment of Sudan's Sovereign Council," they said on Friday.
The statement called for the reinstatement of Prime Minister Abdalla Hamdok, who was briefly detained and later placed under house arrest following the military takeover.
Since the power grab, Burhan has overseen sweeping changes in multiple sectors including in education and banking which were seen by many in Sudan as a way to entrench the military's control.
He insists the military's move on October 25 "was not a coup" but a push to "rectify the course of the transition" as factional infighting and splits deepened between civilians from the FFC and the military under the now-deposed government.
