During fighting between the two forces, US Secretary of State Antony Blinken spoke with Sudanese army chief Abdel Fattah al-Burhan and the head of the paramilitary Rapid Support Forces (RSF), Mohammed Hamdan Dagalo.
Since the fighting began on Saturday, approximately 185 people have been killed.
Mr. Blinken tweeted about the urgent need for a ceasefire and the importance of ensuring the safety of diplomatic personnel and aid workers.
The RSF acknowledged the phone call with Mr. Blinken on its social media page but made no firm commitment to end the fighting.
On Monday night, a second three-hour ceasefire was barely observed, with both sides blaming each other for the breach.
An EU diplomat was assaulted in his official residence, and the UN reported that its agencies, warehouses, and guest houses had been shot at and looted.
Some civilian homes have also been broken into and residents have been assaulted, but RSF has denied any involvement.
The two military leaders disagree on the future of Sudan, including the integration of the RSF into the national army.
