The Ebola crisis in West Africa will take at least six months to bring under control, according to a medical charity.
The president of Medecins Sans Frontieres (MSF), Joanne Liu, said the outbreak, which has killed 1,145 people, was "deteriorating faster, and moving faster, than we can respond to".
The United Nations' health agency, the World Health Organization, had earlier said "extraordinary measures" were needed to tackle the crisis.
The current outbreak began in Guinea in February.
It has since spread to Sierra Leone, Liberia and Nigeria.
Speaking in Geneva, Switzerland, 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.
"In terms of timeline, we're not talking in terms of weeks, we're talking in terms of months.
"We need a commitment for months, at least I would say six months, and I'm being, I would say, very optimistic."
