The truce between Sudan's army and the paramilitary Rapid Support Forces (RSF) is set to expire at midnight local time (2200 GMT). Fighting was reported in Khartoum and Darfur on Thursday.
US Secretary of State Antony Blinken said on Thursday that Washington was working with Sudan's rival factions to extend a ceasefire that is set to expire.
Blinken said he would provide more information "in the coming ours."
The Sudanese Armed Forces said in a statement on Thursday that they had agreed to extend the truce for another 72 hours.
The truce was mediated by the US and Saudi Arabia, according to the statement.
The previous cease-fire between Sudan's army and paramilitaries belonging to the Rapid Support Forces (RSF) is set to expire at midnight local time (2200 GMT).
"We are very actively working to extend the ceasefire," Blinken told reporters. "We've had a 72-hour ceasefire, which like most ceasefires is imperfect but nonetheless has reduced violence," he said.
"That's obviously created somewhat better conditions for people in Sudan," the US official stressed.
Blinken said that the US was also working to establish a more regular route for the evacuation of foreign citizens from Sudan.
Earlier, General Abdel Fattah al-Burhan, who leads Sudan's army, said that he had given initial approval to a proposal by the East African IGAD bloc for another three-day cease-fire. The RSF's position on the proposal was unclear.
The State Department said on Wednesday that Blinken had discussed with African Union Commission Chairperson Moussa Faki Mahamat ways to create a sustainable end to the fighting.