The outbreak of Ebola in West Africa will take at least six months to bring under control, medical charity Medecins Sans Frontieres (MSF) says.
Speaking in Geneva, MSF President Joanne Liu said the situation was "deteriorating faster, and moving faster, than we can respond to".
Earlier, the World Health Organization (WHO) said the scale of the outbreak appeared to be "vastly underestimated".
It said that "extraordinary measures" were needed.
The epidemic began in Guinea in February and has since spread to Liberia, Sierra Leone and Nigeria.
On Friday, the death toll rose to 1,145 after WHO said 76 new deaths had been reported in the two days to 13 August. There have been 2,127 cases reported.
Ms Liu said that although Guinea was the initial epicentre, the pace there had slowed, and other countries - particularly Liberia - were now the focus.
"If we don't stabilise Liberia, we will never stabilise the region," she said.