In the sixth week of the war, witnesses reported a relative calm had taken hold, both in greater Khartoum and in the Darfur region's cities of Nyala and El Geneina, which have been among the other main battlegrounds.
"We have not heard shelling in our neighborhood since last night," said a witness in southern Khartoum.
Residents had reported combat and air strikes in different districts of the capital minutes after the ceasefire formally started at 9:45 pm (1945 GMT) on Monday.
The battles since April 15 have killed an estimated 1,000 people, sparked mass evacuations of foreigners, and forced more than a million people to flee their homes internally and across borders, fuelling concerns for regional stability.
The week-long truce aims to allow desperately needed humanitarian aid for civilians, and restoration of essential services.
United States Secretary of State Antony Blinken said in a video message that the truce is "backed by a remote monitoring mechanism" supported by the US.
"If the ceasefire is violated, we'll know," he said. "And we will hold violators accountable through our sanctions and other tools at our disposal."
Fighting pits the army, led by Sudan's de facto leader Abdel Fattah al-Burhan, against the paramilitary Rapid Support Forces of his former deputy Mohamed Hamdan Daglo.
Those unable to flee have run low on water, food, and basic supplies, and more than half the population, 25 million people, are in need of humanitarian aid, according to the UN.
"Seven days is not a long time if you look at the massive scale of humanitarian emergency in Sudan," International Committee of the Red Cross regional director for Africa, Patrick Youssef, told AFP on Tuesday.
"But we are also in a situation where every minute counts and can provide a much-needed respite," he said.
The text of the truce deal says warring parties agreed to secure "unimpeded road access along designated corridors or routes for humanitarian assistance delivery."
Aid workers are waiting impatiently for those promised corridors to materialize. No permits had been authorized as of Tuesday, one international humanitarian worker told AFP on condition of anonymity, due to safety concerns.
"The whole country is taken hostage," and both parties have "singularly failed" to respect international humanitarian law, the UN's expert on human rights in Sudan, Radhouane Nouicer, said Tuesday.
"People feel alone and abandoned amid a chronic shortage of food, drinking water, homes destroyed, indiscriminate attacks in residential areas and widespread looting."
The pause in fighting longed for by Khartoum residents would also enable more of them to flee the city. The United Nations said nearly 650,000 had already done so during the war, in which numerous ceasefires previously announced were quickly violated.
Before it began, there had been an absence of signals on the ground that the latest truce would be honoured.
Volker Perthes, the UN envoy to Sudan, told the Security Council on Monday that "fighting and troop movements have continued even today, despite a commitment by both sides not to pursue military advantage before the ceasefire takes effect".
The US and Saudi Arabia said this agreement was different because the seven-page document was "signed by the parties" and would be supported by the monitoring mechanism.
Neither side has directly blamed the other for breaking this truce -- as they did within minutes after previous ceasefires collapsed.
But the health ministry released a statement on Tuesday accusing the RSF of violating hospitals.
The ministry, loyal to Burhan, said RSF troops "stationed themselves" inside two hospitals in greater Khartoum Tuesday, "assaulting medical staff and ejecting patients".
The RSF called the accusations "lies".
Major fighting has devastated the Darfur region near Chad, where the UN has reported hundreds of civilians killed in the West Darfur capital El Geneina.
Perthes in his Security Council address warned that "the conflict risks to expand and prolong... with implications for the region."
"In parts of the country, fighting between the two armies or the two armed formations has sharpened into communal tensions, or triggered conflict between communities," he said, after reports of civilians being armed in Darfur.
Sudan has a long history of military coups. The army 2019 overthrew the veteran Islamist autocrat Omar al-Bashir after mass protests against his rule.
Sudanese were promised a gradual transition toward civilian rule, but Burhan and Daglo staged another coup in October 2021 before simmering tensions between the two men flared into the current war.