Ebola death toll passes 1,900, says WHO
There have been 3,500 confirmed or probable cases in Guinea, Sierra Leone and Liberia.
"The outbreaks are racing ahead of the control efforts in these countries," WHO chief Margaret Chan said.
The WHO is meeting on Thursday to examine the most promising treatments and to discuss how to fast-track testing and production.
Disease control experts, medical researchers, officials from affected countries, and specialists in medical ethics will all be represented at the meeting in Geneva.
At least $600m (£360m) is needed to fight the virus, and more than 20,000 people could be infected before the outbreak is brought under control, the WHO has warned.
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," she said.
More than 40% of the deaths have occurred in three weeks leading up to 3 September, the WHO says, indicating that the epidemic is fast outpacing efforts to control it.
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