Witnesses in Khartoum said the situation was "calm".
A 72-hour ceasefire between Sudan's warring generals took effect on Sunday to allow for the delivery of desperately needed aid to the country, on the eve of a humanitarian conference.
The army led by Abdel Fattah al-Burhan has since April 15 been battling paramilitary forces commanded by his former deputy Mohamed Hamdan Daglo, after the two fell out in a bitter power struggle.
Multiple truces have been agreed and broken in the war that has claimed the lives of more than 2,000 people and driven over two million from their homes, including at least 528,000 who fled abroad.
The latest ceasefire came into force at 6:00 am (0400 GMT), with the mediators saying the two sides had agreed to refrain from attacks and allow freedom of movement and the delivery of humanitarian aid.
"The Kingdom of Saudi Arabia and United States of America announce the agreement of representatives of the Sudanese Armed Forces (SAF) and the Rapid Support Forces (RSF) on a ceasefire throughout Sudan for a period of 72 hours," the Saudi foreign ministry said.
Witnesses in Khartoum said the situation was "calm".
"We want a full ceasefire," Sami Omar, who lives in Khartoum's twin city of Omdurman, told AFP.
"A truce is not sufficient for us to return to our lives. They may stop fighting, but the RSF will not leave the homes (they occupy) and passing through checkpoints is just as difficult."
The United Nations will on Monday host an international donors' conference for Sudan in the Swiss city of Geneva.
Intensifying air strikes
Clashes had intensified before both sides pledged to respect the truce in separate statements on Saturday evening.
The RSF said it would abide by the cessation of hostilities, while the army said "despite our commitment to the ceasefire, we will respond decisively to any violations the rebels commit".
Saudi Arabia had threatened on Saturday to "postpone" negotiations on its soil between the two sides "should the parties fail to respect the 72-hour ceasefire".
The talks, which began weeks ago, have so far failed to produce any concrete agreement.
On Saturday, warplanes struck residential districts of Khartoum, killing "17 civilians, including five children", according to a citizens' support committee. AFP was unable to independently confirm the figures.
The RSF accused the army of targeting residential areas and claimed to have shot down a fighter jet.
A video the paramilitary forces posted online showed destroyed homes and blankets covering what appeared to be dead bodies.
Since battles began, the death toll across Sudan has topped 2,000, the Armed Conflict Location and Event Data Project says.
A record 25 million people -- more than half the northeast African country's population -- depends on humanitarian aid, the United Nations says.
'Ominous reminder'
Intense fighting has rocked the western region of Darfur, with the United States saying as many as 1,100 people have been killed in the West Darfur state capital of El Geneina alone.
The Doctors Without Borders (MSF) charity issued an urgent call for more beds and staff across the border in Chad, where it said more than 600 patients -- most with gunshot wounds -- had arrived.
Chadian leader General Mahamat Idriss Deby Itno visited the border town of Adre to assess the scale of "the influx of refugees and ensure that the borders with Sudan are effectively closed", his office said.
The International Organization for Migration says at least 149,000 people have fled from Darfur into Chad, among the roughly 2.2 million uprooted by the fighting.
The United States attributed this week's atrocities in Darfur "primarily" to the RSF and said alleged rights violations were an "ominous reminder" of the region's previous genocide.
A years-long war in Darfur began in 2003 with a rebel uprising that prompted then-strongman Omar al-Bashir to unleash the Janjaweed militia, whose actions led to international charges of genocide, war crimes and crimes against humanity.
The RSF have their origins in the Janjaweed.
Kuwait said on Sunday that it had sent 10 tonnes of food and medical supplies to Sudan.
(Except for the headline, this story has not been edited by NDTV staff and is published from a syndicated feed.)