Fighting in Sudan eased on Tuesday and more foreigners and locals fled the capital Khartoum, where marauding combatants created what a U.N. agency said was a "high risk of biological hazard" by seizing a laboratory.
The World Health Organization said one of the warring parties had taken control of a national health facility that stores measles and cholera pathogens for vaccinations, and ejected the technicians.
It gave few details and did not say which of the two sides - the army or the paramilitary Rapid Support Forces (RSF)- had captured the lab, which also contains a major blood bank.
An exodus of embassies and aid workers from Africa's third largest country has raised fears that civilians who remain will be in greater danger if an alternative to hostilities is not found before a three-day truce ends on Thursday.
Yassir Arman, a leading figure in a civilian political coalition, the Forces for Freedom and Change (FFC), urged humanitarian groups and the international community to help restore water and electricity, and send generators to hospitals.
"There are bodies scattered in streets and sick people who cannot find medicine, no water nor electricity. People should be allowed to bury their dead during the ceasefire," he said.
One Khartoum resident, who declined to give his name, said he feared that with fewer international observers, fighting forces would show less respect for civilians.
The United Nations humanitarian office said it had cut back activities due to the fighting. The U.N. refugee agency forecast that hundreds of thousands of people might flee into neighbouring countries.
Since the warfare erupted on April 15, tens of thousands have already left for neighbouring Chad, Egypt, Ethiopia and South Sudan, despite the uncertainty of conditions there.
With civilians leaving Khartoum in cars and buses, the streets of one of Africa's biggest metropolitan areas were largely emptied of ordinary daily life, with those still in the city huddling at home.
