The Ebola outbreak in West Africa has killed 2,288 people, with half of them dying in the last three weeks, the World Health Organization (WHO) says.
It said that 47% of the deaths and 49% of the total 4,269 cases had come in the 21 days leading up to 6 September.
The health agency warned that thousands more cases could occur in Liberia, which has had the most fatalities.
The outbreak, which was first reported in Guinea in March this year, has also spread to Sierra Leone and Nigeria.
In Nigeria, eight people have died out of 21 cases, while one case of Ebola has been confirmed in Senegal, the WHO said in its latest update.
On Monday, the agency called on organisations combating the outbreak in Liberia to scale up efforts to control the outbreak “three-to-four fold”.
Ebola spreads between humans by direct contact with infected blood, bodily fluids or organs, or indirectly through contact with contaminated environments.
However, the WHO says conventional means of controlling the outbreak, which include avoiding close physical contact with those infected and wearing personal protective equipment, were not working well in Liberia.
Meanwhile, the US says it will help the African Union mobilise 100 African health workers to the region and contribute an additional $10m (£6.2m) in funds to deal with the outbreak.
The announcement comes as a fourth US aid worker infected with the deadly virus was transported to a hospital in Atlanta for treatment.
Two other aid workers who were treated at the same hospital have since recovered from an Ebola infection.