The International Federation of Red Cross and Red Crescent Societies (IFRC) said the three volunteers likely contracted the virus on 27 March while carrying out body management work during a humanitarian mission unrelated to Ebola. At the time, the outbreak had not yet been identified.

“These volunteers lost their lives while serving their communities with courage and humanity,” the IFRC said.

Ajiko Chandiru Viviane, Sezabo Katanabo and Alikana Udumusi Augustin – volunteers with the Mongbwalu branch in Ituri province in north-eastern Congo – died on 5, 15 and 16 May respectively. They are believed to be among the first known victims of the latest outbreak.

Health experts warn the bodies of Ebola victims can remain highly infectious after death, with bodily fluids capable of spreading the virus.

The outbreak involves the rare Bundibugyo strain of Ebola, which has no proven vaccine and has a fatality rate of around one in three.

On Friday, the World Health Organization (WHO) raised the public health risk in DR Congo from “high” to “very high”. WHO Director-General Dr Tedros Adhanom Ghebreyesus said the regional risk across Africa was also high, though the global threat remained low.

Uganda confirmed three additional cases on Saturday, bringing its total to five. The Africa Centres for Disease Control and Prevention warned that 10 other countries could also be at risk: Angola, Burundi, the Central African Republic, the Republic of Congo, Ethiopia, Kenya, Rwanda, South Sudan, Tanzania and Zambia.

The DR Congo has suspended all commercial and private flights to and from Bunia – the capital of Ituri province, where most cases and deaths have been reported – in an effort to prevent cross-border transmission.

“Humanitarian, medical or emergency flights will only be authorised after special approval from the aviation and health authorities,” the transport ministry said.

Local media also reported that Ituri’s military governor had banned gatherings of more than 50 people and suspended funeral wakes. Burials can now only be conducted by designated “safe and dignified” burial teams.

Elsewhere in the province, Médecins Sans Frontières (MSF) said a tent supporting the Ebola response in Mongbwalu was burned down on Friday.

The incident came a day after an angry crowd in another part of Ituri set fire to part of a hospital after relatives of a young man believed to have died from Ebola were prevented from taking his body for burial.

MSF said: “Understandably, there are still many uncertainties and fears among the community in this rapidly evolving context.

“This incident highlights just how critical sustained community engagement and trust-building are.”

Cases have also been detected in North and South Kivu, where fighting between government forces and M23 rebels is complicating efforts to contain the outbreak.

A vaccine could be six to nine months away experts have said.