WASHINGTON: US President Barack Obama urged against “hysteria or fear” Saturday in the face of a growing Ebola crisis, as the United Nations spoke of an “encouraging” response to its funding appeal.

The worst-ever outbreak of the deadly virus has so far killed more than 4,500 people, mainly in three West African nations at the epicenter of the outbreak: Guinea, Liberia and Sierra Leone.

Obama’s warning came a day after the World Bank warned the battle against the disease was being lost and as the US president named an “Ebola czar” to coordinate Washington’s response.

A UN appeal for nearly $1 billion to fight the spread of the disease has so far fallen short, but a spokesman said more money was coming in daily.

Out of $988 million requested a month ago, the UN said Saturday $385.9 million had already been given by a slew of governments and agencies, with a further $225.8 million promised.

“It has been encouraging to see the amount and the speed with which these amounts have been committed,” said Jens Laerke, spokesman for the UN’s humanitarian office (OCHA).

“To be honest, I don’t recall during my time at OCHA that we have had such a response within a month for a billion-dollar appeal.” Nevertheless, Laerke said, this wasn’t a sign the need for donations had passed.

“Nobody’s smiling in this crisis, so I’m not going to go out and clap my hands and say everything is going fine, because it’s not,” he said.

The World Health Organization promised on Saturday that it would publish a full review of its handling of the Ebola crisis once the outbreak was under control, in response to a leaked document that appeared to acknowledge it had failed to do enough.

The WHO said in a statement that it would not comment on an internal document cited in an Associated Press story on Friday, saying it was a first draft that had not been fact-checked and was “part of an on-going analysis of our response.”

“We cannot divert our limited resources from the urgent response to do a detailed analysis of the past response. That review will come, but only after this outbreak is over,” the organization said.

The WHO has been widely criticized for its slow response to the epidemic and its early reassurances, despite repeated public warnings from the medical charity Medecins Sans Frontieres, which was leading the fight against the virus on the ground.