More than 1900 people have now died in West Africa's Ebola outbreak, the World Health Organisation (WHO) says.
Forty per cent of the deaths have occurred in three weeks leading up to 3 September.
WHO head Margaret Chan said there were 3500 confirmed or probable cases in Guinea, Sierra Leone and Liberia. "The outbreaks are racing ahead of the control efforts in these countries," she said.
The organisation is holding a meeting in Geneva to examine the most promising treatments and to discuss how to fast track their testing and production, the BBC reports. Disease control experts, medical researchers, officials from affected countries, and specialists in medical ethics will be represented.
The WHO has previously warned that more than 20,000 people could be infected before the outbreak of the virus is brought under control.
Ms Chan described the outbreak as "the largest and most severe and most complex we have ever seen".
"No one, even outbreak responders with experience dating back to 1976, to 1995, people that were directly involved with those outbreaks, none of them have ever seen anything like it," Ms Chan said.
On Wednesday Nigeria reported two further cases in the city of Port Harcourt.
There had previously only been one case outside the city of Lagos, where five people have died from the virus.
Also on Wednesday, the first British person to contract Ebola during the outbreak was discharged from hospital after making a full recovery.
On Tuesday medical charity Medecins Sans Frontieres warned that a global military intervention was needed to combat the outbreak.
It has called for military and civilian teams capable of dealing with a biological disaster to be deployed immediately, as well as for more field hospitals with isolation wards to be set up, trained healthcare workers to be sent to the region and air support to move patients and medics across West Africa.