The Ebola outbreak in West Africa is spreading faster than efforts to control it, World Health Organization (WHO) head Margaret Chan has said.
She told a summit of regional leaders that failure to contain it could be "catastrophic" in terms of lives lost.
Ebola death toll in West Africa reaches 729, two US aid workers in grave condition http://t.co/NUEo8gU2o0— प्रदीप K Paijwar ® (@paijwar) August 1, 2014
But she said the virus, which has claimed 729 lives in four West African countries since February, could be stopped if well managed.
Ebola kills up to 90% of those infected.
It spreads by contact with infected blood, bodily fluids, organs - or contaminated environments.
Dr Chan was meeting the leaders of the worst-affected countries - Guinea, Liberia and Sierra Leone - to launch a new $100m (£59m; 75m euro) Ebola response plan.
"This meeting must mark a turning point in the outbreak response," Dr Chan said at the summit in Guinea's capital, Conakry.
African leaders to launch $100m Ebola battle plan http://t.co/Yxr5tYL5J6— Agence France-Presse (@AFP) August 1, 2014
"Cases are occurring in rural areas which are difficult to access, but also in densely populated capital cities," she said, explaining that the outbreak was the world's deadliest and largest in terms of geographical areas.