Rwanda says eight people have died so far from the highly contagious Marburg virus.
The announcement comes days after the country declared an outbreak of deadly hemorrhagic fever for which there is no approved vaccine or treatment.
Like Ebola, the Marburg virus originates from fruit bats and is spread between people through close contact with the bodily fluids of infected people.
Rwanda, a landlocked country in central Africa, declared an outbreak of violence on Friday and a day later the first six deaths were reported.
Health Minister Sabin Nsanzimana said on Sunday night, so far, 26 cases have been confirmed, and eight of the sick have died.
“WHO considers the risk of an outbreak to be very high at the national level, high at the regional level and low at the global level,” WHO said on Monday. “Investigations are ongoing to determine the full extent of the outbreak and this risk assessment will be updated as more information is received.”