Equatorial Guinea has confirmed eight more cases of the Marburg virus disease, bringing the total to nine since February when it was first declared.
the cases of the viral haemorrhagic fever were confirmed following laboratory analysis of additional samples.
It noted that there were 20 probable cases and deaths.
The new cases were reported from areas bordering Cameroon and Gabon.
The cases are from areas that are 50km (31 miles) apart, with the WHO suggesting a wider transmission of the virus.
It said it was working with national authorities to step up emergency response measures.
It comes days after Tanzania, on the other side of the continent, confirmed eight cases of the viral disease – including five deaths.
Marburg is transmitted to people from fruit bats and spreads among humans through direct contact with the bodily fluids of infected people, surfaces and materials.