Sudan's rival generals resumed shelling and gunfire in the capital Khartoum Sunday after the clock ran out on the 24-hour cease-fire.

Deadly fighting has raged in the northeast African country since mid-April, when army chief Abdel Fattah al-Burhan and his former deputy Mohamed Hamdan Daglo, who commands the paramilitary Rapid Support Forces (RSF), turned on each other.

The latest in a series of cease-fire agreements enabled civilians trapped in the capital Khartoum to venture outside and stock up on food and other essential supplies.

But only 10 minutes after it ended at 6 a.m. (4 a.m. GMT) on Sunday the capital was rocked again by the sound of shelling and clashes, witnesses told AFP.

Heavy artillery fire was heard in Khartoum and its twin city Omdurman to the north, and fighting also erupted on al-Hawa Street, a major artery in the south of the capital, the witnesses said.

Multiple truces have been agreed and broken since the fighting started, and Washington had slapped sanctions on both rival generals after the last attempt collapsed at the end of May.

The latest nationwide cease-fire was announced by U.S. and Saudi mediators who warned they may break off mediation efforts.

"Should the parties fail to observe the 24-hour cease-fire, facilitators will be compelled to consider adjourning" talks in the Saudi city of Jeddah which have been suspended since late last month, the mediators said Saturday.

The mediators said they "share the frustration of the Sudanese people about the uneven implementation of previous cease-fires."

Upwards of 1,800 people have been killed in the fighting, according to the Armed Conflict Location and Event Data Project.

Nearly 2 million people have been displaced, including 476,000 who have sought refuge in neighboring countries, the United Nations says.