The World Health Organization says it has suspended its work to contain the outbreak of the deadly Marburg virus in Angola following attacks on staff.
The WHO said people in northern Uige province, where most of the cases have been reported, had attacked its mobile surveillance vehicles.
Locals may believe WHO staff had brought the disease, an official said.
More than 200 Marburg cases have been reported since October and most of the victims have died.
The haemorrhagic fever caused by Marburg is similar to the Ebola virus, but United Nations health experts say it appears to have an even higher mortality rate.
The WHO said the attacks meant its mobile surveillance teams had been unable to investigate reports of several new deaths in the region.
The organisation did not say when it would be able to resume its operations.
It said it was in discussions with provincial authorities to find an urgent solution.
Richard Thompson, WHO's spokesman on communicable diseases, told the Reuters news agency: "We are very concerned because you can begin counting every day lost in terms of how many people die."
He added: "This kind of reaction from local people is not uncommon in a haemorrhagic fever outbreak. They sometimes believe that it is the medicine people who have brought the illness to their communities."
Early symptoms of Marburg are diarrhoea, stomach pains, nausea and vomiting, which give way to bleeding.
Marburg has no known vaccine or medical treatment.