WHO Assistant Director General Bruce Aylward said the epidemic was spreading geographically and the number of cases would grow and exceed 9,000 by the end of this week.
He added that although in certain areas the WHO was "seeing disease coming down but that doesn't mean they will get to zero."
Aylward said the WHO was still focused on treating Ebola patients, handing out protective equipment to families and setting up clinics in the affected countries.
The World Health Organization describes Ebola virus disease (formerly known as Ebola haemorrhagic fever) as a severe, often fatal illness, with a case fatality rate of up to 90%. Symptoms include sudden onset of fever, intense weakness, muscle pain, headache and sore throat. This is followed by vomiting, diarrhoea, rash, impaired kidney and liver function, and in some cases, both internal and external bleeding. The infection is transmitted by direct contact with the blood, body fluids and tissues of infected animals or people. People are infectious as long as their blood and secretions contain the virus. The incubation period is 2 to 21 days. There is no known cure or vaccine for the disease. The only treatment offered is “supportive intensive care.” During an outbreak, those at higher risk of infection are health workers, family members and others in close contact with sick people and deceased patients.