Air strikes killed 17 civilians, including five children, in the capital Saturday, a citizens' group said, as medics in Chad reported hundreds of wounded from Darfur seeking treatment.
Multiple truces have been agreed and broken during the two-month war, including after the United States slapped sanctions on both generals after a previous attempt collapsed at the end of May.
A 24-hour ceasefire from June 10 to June 11 provided Khartoum residents with a brief respite from the air strikes and artillery exchanges that have ravaged whole neighbourhoods of the capital but the fighting resumed within 10 minutes of the ceasefire ending.
"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," a Saudi foreign ministry statement said late Saturday.
The ceasefire is due to take effect at 6 am (0400 GMT), the mediators said.
"The two sides agreed that during the ceasefire period they would refrain from movements and attacks, the use of warplanes or drones, artillery bombardment, reinforcement of positions, resupply of forces, or refrain from attempting to achieve military gains," the mediators said.
"They also agreed to allow freedom of movement and the delivery of humanitarian aid throughout Sudan."
The SAF, commanded by Abdel Fattah al-Burhan, has since April 15 been battling the paramilitary RSF, headed by his former deputy Mohamed Hamdan Daglo, after the two fell out in a power struggle.
A record 25 million people -- more than half Sudan's population -- are in need of aid, the United Nations says.
Intensifying air strikes
Witnesses say air strikes have intensified in the capital over the past few days.
On Saturday, warplanes struck several residential districts of Khartoum, killing "17 civilians, including five children", according to a citizens' support committee. AFP was not immediately able to independently confirm the committee's figures.
Residents had earlier reported air strikes around the city's southern Yarmouk district -- home to a weapons manufacturing and arms depot complex where the RSF claimed "full control" in early June.
In a video published Friday on the army's Facebook page, deputy army chief Yasser Atta warned civilians to keep away from houses where the RSF are located because the army "will attack them at any time".
Since battles began, the death toll across the country has topped 2,000, the Armed Conflict Location and Event Data Project said.
'Ominous reminder'
Hundreds of kilometres (miles) west of Khartoum, up to 1,100 have been killed in the West Darfur state capital El Geneina alone, according to the US State Department.
Medics in Chad said Saturday they were overwhelmed by the hundreds of wounded fleeing Sudan's Darfur region, which has become an increasing focus of global concern.
The dead have included West Darfur Governor Khamis Abdullah Abakar, killed after he criticised the paramilitaries in a Wednesday television interview. The RSF denied responsibility.
"We are overwhelmed in the operating theatre. We urgently need more beds and more staff," said Seybou Diarra, a physician and project coordinator in Adre, Chad, for the Doctors Without Borders (MSF) charity.
"As violence rages in West Darfur, wounded people are coming in waves" to the hospital in Adre, just over the border about 20 kilometres (12 miles) west of El Geneina, the MSF statement said.
More than 600 patients, most with gunshot wounds, arrived at the facility over a three-day period -- more than half of them on Friday, it said.
Claire Nicolet, MSF's head of emergency programmes, cited "reports of intensifying and large-scale attacks this week".
According to the International Organization for Migration (IOM), at least 149,000 people have fled from Darfur into Chad.
They are among the roughly 2.2 million people uprooted nationwide by the fighting, which has forced more than 528,000 to seek refuge in neighbouring countries, IOM said.
On Thursday, the State Department attributed the atrocities in Darfur "primarily" to the RSF and said the violence and alleged rights violations are 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.
