The lab is located in central Khartoum, close to flashpoints of the fighting that have seen dozens of hospitals shut down in the capital and elsewhere across Sudan.

The World Health Organization on Tuesday warned of a “huge biological risk” after Sudanese fighters seized control of the National Public Health Laboratory in the capital of Khartoum, calling it an “extremely dangerous” development.

The warning came as United Nations officials warned more refugees could flee Sudan despite a US-brokered ceasefire between the Sudan Armed Forces (SAF) and the Rapid Support Forces (RSF), a paramilitary group battling the army for control of the country.

Gunfire and the roar of fighter jets were heard Tuesday in Khartoum, half a day after the announcement of a 72-hour truce raised hopes of opening up escape routes for civilians desperate to flee. Heavy clashes erupted between the SAF and RSF in Khartoum’s northern part.

The two warring sides have accused each other of violating the agreement.

The number of people killed in Sudan since fighting began eleven days ago has reached at least 459 deaths, the WHO also said Tuesday, with at least 4,072 people injured.

The violence has plunged Sudan into chaos, pushing the already heavily aid-dependent country to the brink of collapse. Before the clashes, the UN estimated that a third of Sudan’s population, about 16 million people, was in need of assistance.

Nima Saeed Abid, the WHO representative in Sudan, expressed concerns that “one of the fighting parties” had seized control of the laboratory, which contains samples of diseases and other biological material, and “kicked out all of the technicians”. The WHO did not appoint blame for the lab seizure.

“That is extremely, extremely dangerous because we have polio isolates in the lab, we have measles isolates in the lab, we have cholera isolates in the lab,” Abid said. “There is a huge biological risk associated with the occupation of the central public health lab in Khartoum by one of the fighting parties.”

The WHO said the expulsion of technicians and power cuts that the facility had suffered meant that “it is not possible to properly manage the biological materials that are stored in the lab for medical purposes.”

The power cuts also mean there is a risk of spoilage of depleting stocks of blood bags, the laboratory’s director-general said.

“If the violence does not stop, there is a danger that the health system will collapse,” the UN agency warned Friday.