Buildings have caught fire in Sudan's capital after heavy fighting between the army and rival forces.
Videos posted online on Sunday showed the iconic Greater Nile Petroleum Oil Company Tower engulfed in flames.
"This is truly painful," said Tagreed Abdin, an architect of the building, in a post on X, formerly known as Twitter.
Air strikes and ground battles have continued in Khartoum and other towns and cities since fighting broke out in April.
Over one million people have been forced to flee the country, the UN has said.
Located near the River Nile, the 18-storey oil firm skyscraper is one of the most recognisable landmarks in Khartoum.
Ms Abdin said it defined the skyline of the city, and lamented "such senseless destruction".
It is not yet clear what caused the building's cone-like structure, which has a glass facade, to catch fire. There have been no reports of injuries or deaths.
The violence in Sudan began on 15 April, triggered by a power struggle between the leaders of the Sudanese army and the paramilitary Rapid Support Forces (RSF).
It followed days of tension as members of the RSF were redeployed around the country in a move that the army saw as a threat.
The Sudan War Monitor, which provides analysis of the conflict, said the RSF had attacked areas controlled by the army on Saturday, including an office block at the justice ministry. Several government buildings are reported to have caught fire as a result of the attack.
The RSF said the army carried out the attacks, including on the 18-storey skyscraper.
The army has not yet commented.
The former vice president of the Greater Nile Petroleum Operating Company, Fadl Abdullah, told BBC Arabic that building had been constructed at a cost of about $20m (£16m), and its destruction was a "very great financial loss".
Attacks on army premises continued into Sunday, witnesses told AFP news agency.
Residents in a southern district of the city - where the army was targeting RSF bases - told AFP they heard "huge bangs" as they woke up.
Health authorities announced on Sunday that all the main hospitals in Khartoum - as well as the Darfur region - were out of service.
Nawal Mohammed, 44, who lives at least 3km (1.8 miles) from clashes in the capital, said the doors and windows of her family home shook with the force of explosions.
She described the battles on Saturday and Sunday as "the most violent since the war began".
According to a group of pro-democracy lawyers, the fighting had killed "dozens of civilians" in Khartoum since Friday.
Fighting was also reported in the city of El-Obeid, some 400km (250 miles) south of the city.
The RSF has been fighting to take control of the capital, and the military's air strikes have been aimed at weakening RSF positions.
The conflict has killed around 7,500 people and displaced more than five million.