Following the death of two people and two cases of infection, there are fears that hundreds may have been exposed to the Ebola virus in Mali.
The WHO, the Mali government and the US Centers for Disease Control and Prevention are calling for ramping up efforts to avert an epidemic in the poor country.
The CDC is particularly alarmed by a cluster of new cases reported from a hospital in Bamako where a priest and nurse who treated him died, reports NPR.
"This is not just one case," said Tom Frieden, director of the CDC. "It's a cluster."
The cluster could well blow up into a full-scale outbreak, warned the CDC, calling for tracing and monitoring all contacts.
According to Doctors Without Borders, healthcare workers in Mali are new to Ebola and will have to be trained while international support will have to be stepped up quickly to control the situation.
Earlier, all those who had come in contact with the nurse were placed under a 21-day quarantine.
The current epidemic has claimed over 5,000 lives in the three West Africa nations of Liberia, Sierra Leone and Guinea. Liberia seems to have emerged after facing a severe crisis forced by a weak infrastructure and poor facilities.