The World Health Organisation (WHO) said on Friday that 4,033 people are known to have died in the worst Ebola outbreak on record, out of 8,399 cases.
It added that the virus had become “entrenched” in the capital cities of the worst affected West African countries.
The UN has said its billion-dollar appeal to fight Ebola has only been partially funded.
The charity Médecins Sans Frontières/Doctors Without Borders says there has been a sudden sharp increase in suspected Ebola cases in Guinea.
Its treatment centre at Guéckédou near the Liberian border is the epicentre of the epidemic which began in March.
By July case numbers had appeared to go down in the West African country, suggesting the end of the outbreak might be near.
But since the beginning of October a rise in the number of patients has been reported both at Guéckédou, and particularly in the capital Conakry, the first major West African city to be affected.
MSF is now caring for 120 people in the two locations, of whom 85 are confirmed to have the virus.
Dr Bruce Aylward, the WHO’s Assistant Director-General, speaking from Sierra Leone, predicted that Ebola would be brought under control.
“We have to look at how people bury people, how they care for the sick in this country, and you have to do that against the background and backdrop of a very weak health system. It takes a long time to change practices which have evolved over hundreds, perhaps thousands of years. So these things are going to take time, and the virus is not giving them very much time,” he said.
Europe has also become embroiled but the European Commission health spokesman has said it’s “highly improbable” that Ebola will spread further across the continent.
In France a possible case reported at a Paris hospital turned out to be a false alarm.
The prime minister has warned the authorities and the media not to provoke panic among the population.
An information hotline is being set up from this weekend. Tighter checks at French airports are likely in the coming days.
Numerous countries, including the UK, say they are boosting their screening of passengers for signs of Ebola.