GENEVA: The number of Ebola cases in West Africa could start doubling every three weeks and it could end up costing nearly $1 billion to contain the crisis, the World Health Organisation warned Tuesday.

Even as President Barack Obama was expected to announce the deployment of 3,000 American troops to help provide aid in the region, Doctors Without Borders told the UN health agency that the global response to Ebola was falling far short of what is needed.

“The response to Ebola continues to fall dangerously behind,” Joanne Liu, president of the medical charity, told a meeting at the United Nations in Geneva.

“The window of opportunity to contain this outbreak is closing. We need more countries to stand up, we need greater deployment, and we need it now.“

In a report released Tuesday, WHO said some $987.8 million is needed for everything from paying health workers and buying supplies to tracing people who have been exposed to the virus, which is spread by contact with bodily fluids like blood, urine or diarrhea.

Some $23.8 million alone is needed to pay burial teams and buy body bags, since the bodies of Ebola victims are highly infectious and workers must wear protection suits. Nearly 5,000 people have been sickened by Ebola in Liberia, Sierra Leone, Guinea, Nigeria and Senegal since it was first recognized in March.

WHO says it anticipates that figure could rise to more than 20,000. At least 2,400 people have died, with Liberia bearing the brunt of the fatalities.

Recent weeks have seen a flurry of promises of aid. In addition to the US troops, the UN health agency said China has promised to send a 59-person mobile laboratory team to Sierra Leone that includes lab experts, epidemiologists, doctors and nurses.

Britain is also planning to build and operate an Ebola clinic in Sierra Leone, and Cuba has promised to send the country more than 160 health workers.

Still, hospitals and clinics in West Africa are now turning the sick away because they don't have enough space to treat everyone, a sure-fire way to increase the spread of the disease, which in this outbreak is killing about half of those it infects.

The United States, in particular, drew criticism last week when it promised to set up a 25-bed field hospital in Liberia that would only serve foreign health workers.

Many thought the contribution was discriminatory and paltry, given that experts were saying Liberia needed at least 500 more treatment beds.