Sudan's warring generals agreed a new 72-hour ceasefire from Sunday, U.S. and Saudi mediators said, after fighting intensified with deadly air strikes in Khartoum and an exodus of wounded from Darfur over the border into Chad.

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.