There is a “high risk of biological hazard” in the Sudanese capital Khartoum after one of the warring parties seized a laboratory holding measles and cholerapathogens and other hazardous materials, the World Health Organisation said on Tuesday.

Speaking to reporters in Geneva via video link from Sudan, the WHO’s Nima Saeed Abid said technicians were unable to access the National Public Health Laboratory to secure the materials.

“This is the main concern: no accessibility to the lab technicians to go to the lab and safely contain the biological material and substances available,” he said, declining to specify which side had seized the facility.

Fighting erupted between the Sudanese armed forces and Rapid Support Forces (RSF) paramilitaries on April 15 and has killed at least 459 people and injured 4,072, according to the WHO’s latest figures.

The clashes have paralysed hospitals and other essential services and left many stranded in their homes with dwindling supplies of food and water.

The UN humanitarian office (OCHA) has been forced to cut back on some of its activities in parts of Sudan due to intense fighting.

At least five aid workers have been killed since fighting broke out and the two UN agencies who lost staff, the International Organisation for Migration and the World Food Programme, have suspended their activities.

“In areas where intense fighting has hampered our humanitarian operations, we have been forced to reduce our footprint,” said Jens Laerke, spokesperson for the OCHA. “But we are committed to continuing to deliver for the people of Sudan.”