President Joe Biden said the US was temporarily suspending operations at its embassy in Khartoum but remained committed to the Sudanese people, reiterating calls for a ceasefire that have so far gone largely unheeded.
"The belligerent parties must implement an immediate and unconditional ceasefire, allow unhindered humanitarian access, and respect the will of the people of Sudan," Biden said in a statement.
Reuters reports live TV feeds showed thick smoke still hanging over the capital, Khartoum, and its sister cities of Bahri and Ombdurman, as gunfire continued to ring out in some areas, a Reuters reporter said.
The fighting erupted in Khartoum and other parts of the country on 15 April, four years after long-ruling autocrat Omar al-Bashir was toppled during a popular uprising, and has killed more than 400 people.
It pits Sudan's army against the paramilitary Rapid Support Forces (RSF), who jointly staged a coup in 2021 but fell out during negotiations over a plan to form a civilian government and integrate the RSF into the armed forces.
The army under Abdel Fattah al-Burhan and the RSF, headed by Mohamed Hamdan Dagalo, known as Hemedti, have failed to observe ceasefires agreed almost daily, including a three-day truce for the Muslim holiday of Eid al-Fitr, which began on Friday.
Intense fighting has continued around the army's headquarters in central Khartoum and the airport, which has been closed by the clashes, and over the past two days in Bahri, where the army has used troops on the ground as well as air strikes to try to push back the RSF.
The RSF said on Sunday that its forces were targeted by air strikes in Bahri's Kafouri district and that dozens were "killed and injured".
"We strongly condemn this treacherous behaviour, which is inconsistent with the declared commitment to the 72-hour truce," the RSF said in a statement.
People fleeing street battles between the forces of two rival Sudanese generals, wait with their belongings along a road in the southern part of Khartoum, on April 21, 2023. Photo: AFP