Fighting erupted again in Sudan late Tuesday, despite the warring groups’ announcement of a ceasefire, as a U.N. envoy claimed the truce was largely holding despite little evidence that the two sides were ready for substantive discussions.

After discussions mediated by the United States and Saudi Arabia, the Sudan Armed Forces (SAF) and paramilitary Rapid Support Forces (RSF) agreed to a 72-hour truce beginning on Tuesday.

But gunfire and explosions could be heard after nightfall in Omdurman, one of Khartoum’s sister cities on the Nile River where the army used drones to target RSF positions, a Reuters reporter said.

The army also used drones to try to drive fighters back from a fuel refinery in Bahri, the third city at the confluence of the Blue Nile and White Nile.

U.N. special envoy on Sudan Volker Perthes told the U.N. Security Council on Tuesday that the ceasefire “seems to be holding in some parts so far.”

But he said that neither party showed readiness to “seriously negotiate, suggesting that both think that securing a military victory over the other is possible.”

“This is a miscalculation,” Perthes said, adding that Khartoum’s airport was operational but the tarmac damaged.

Since Sudan erupted in warfare between the army and the RSF on April 15, derailing a transition to civilian democracy, the paramilitaries have embedded themselves in residential districts and the army has sought to target them from the air.

The fighting has turned residential areas into battlefields. Air strikes and artillery have killed at least 459 people, wounded over 4,000, destroyed hospitals and limited food distribution in a nation where a third of its 46 million people rely on food aid.

A projectile hit Al-Roumi medical center in Omdurman on Tuesday and exploded inside the facility, injuring 13 people, a hospital official said.