KHARTOUM--Sudan's two warring factions said on Thursday they would prolong a ceasefire agreement by 72 hours, but violence again rocked the capital Khartoum and the western region of Darfur as the U.S. said ceasefire violations were worrying. Hundreds have died and tens of thousands of people have fled for their lives in two weeks of conflict between the army and its rival, the paramilitary Rapid Support Forces (RSF). Together, they toppled a civilian government in an October 2021 coup but are now locked in a power struggle that has derailed an internationally backed transition to democracy and is threatening to destabilise a fragile region. The army on Wednesday said it agreed to a new three-day ceasefire through Sunday following one due to expire on Thursday night. On Thursday, the military reiterated it would extend the truce and said it would honour it unilaterally. Responding for the first time, the RSF said on Thursday it too approved another 72-hour truce starting Friday. The news was welcomed by the United Nations, the African Union, African trade bloc IGAD and the so-called quad countries of the U.S., U.K., Saudi Arabia and UAE. "We also welcome their readiness to engage in dialogue toward establishing a more durable cessation of hostilities and ensuring unimpeded humanitarian access," they said in a joint statement. The army said it controls most of Sudan's regions and is defeating a large RSF deployment in Khartoum where some residential areas have turned into war zones. Despite a partial lull in fighting since the first 72-hour ceasefire started, air strikes and anti-aircraft fire could be heard on Thursday in the capital and the nearby cities of Omdurman and Bahri, witnesses and Reuters journalists said. The White House said it was deeply concerned by the ceasefire violations. It said the situation could worsen at any moment and urged U.S. citizens to leave within 24 to 48 hours. Fighting has spread to the vast Darfur region, where conflict has simmered ever since civil war erupted two decades ago. The Darfur Bar Association, a rights group, said at least 52 people had died in attacks by well-armed "militias" on residential neighbourhoods in the city of El Geneina, as well as its main hospital, main market, government buildings and several shelters for internally displaced people. Militiamen from nomadic Arab tribes entered El Geneina as the fighting between the RSF and army created a security vacuum in recent days, said one resident, who asked to withhold his name due to fear of retribution. They were met with armed members of the Masalit tribe, with clashes extending across the city, causing a new wave of displacement. El Geneina, Sudan's western-most city, has been the site of repeated tribal conflicts in recent years, leading to people being pushed out of their homes multiple times. "In the past, it would be in one neighbourhood and the authorities would get involved," the resident said. "But because of what's going on, there's been no intervention." At least 512 people have been killed and close to 4,200 wounded by the fighting since April 15. The conflict has limited food distribution in the vast nation, Africa's third largest, where a third of the 46 million people were already reliant on humanitarian aid. The top U.N. aid official in Sudan, Abdou Dieng, said "very little can be done" in terms of humanitarian assistance. "We're extremely worried about food supply," Dieng told reporters in New York via phone from Port Sudan where most senior U.N. staff had relocated. The Sudan Doctors' Union said 60 of 86 hospitals in conflict zones had stopped operating. Many foreigners remain stuck in Sudan despite the evacuation of thousands. Sudanese civilians, who have been struggling to find food, water and fuel, were streaming out of Khartoum.