Tom Frieden, director of the US-based Centres for Disease Control, said the epidemic would need an "unprecedented" response to bring it under control.
Health ministers from the Economic Community of West African States will meet in Ghana's capital Accra on Thursday to discuss the region's response to the crisis.
The World Health Organisation (WHO) says the outbreak has already killed 1,427 people. The WHO has said that it is the largest ever Ebola epidemic and has infected an estimated 2,615 people.
Liberia has been hardest-hit of the affected countries, with 624 deaths and 1,082 cases since the start of this year.
The virus is not airborne and is spread when humans come into contact with bodily fluids such as sweat and blood of those infected with virus.
Till date, there is no vaccine or cure for the Ebola virus outbreak, the BBC said.