WATCH: State Department holds briefing as tenuous cease-fire in Sudan enters second day

The State Department held a news briefing on Tuesday as U.N. officials said that one side in the Sudan conflict has seized control of a national health lab in the capital of Khartoum that holds biological material, calling it an “extremely dangerous” development.

Watch the briefing in the player above.

The announcement came as officials warned that more refugees could flee Sudan despite a cease-fire between rival forces.

The fighting has plunged Sudan into chaos, pushing the already heavily aid-dependent African nation to the brink of collapse. Before the clashes, the U.N. estimated that a third of Sudan’s population — or about 16 million people — needed assistance, a figure that is likely to increase.

Dr. Nima Saeed Abid, the World Health Organization’s representative in Sudan, expressed concerns that “one of the fighting parties” — he did not identify which one — had seized control of the central public health laboratory in Khartoum and “kicked out all of the technicians.”

“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,” he told a U.N. briefing in Geneva by video call from Port Sudan. “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 expulsion of technicians and power cuts in Khartoum mean “it is not possible to properly manage the biological materials that are stored in the lab for medical purposes,” WHO said.

The lab is located in central Khartoum, close to flashpoints of the fighting that pits Sudan’s military against the Rapid Support Forces, a paramilitary group that grew out of the notorious Janjaweed militias implicated in atrocities in the Darfur conflict.

Since the outbreak of fighting on April 15, at least 20,000 Sudanese have fled into Chad. Some 4,000 South Sudanese refugees who had been living in Sudan have returned to their home country, U.N. refugee agency spokeswoman Olga Sarrado said.

The figures could rise, she cautioned. Sarrado did not have numbers for the five other countries neighboring Sudan, but the UNHCR has cited unspecified numbers of those fleeing Sudan arriving in Egypt.