The experimental drug ZMapp, which is being used to treat two Ebola-infected Americans, is being sought by African governments trying to contain the outbreak.

American officials insisted that the drug is not a cure, and that it was not tested in human patients before the current crisis.

"We don't even know if it works," Dr Anthony Fauci of the National Institutes of Health (NIH) insisted, Fox reports The NIH was one of the organisations that provided funds to develop ZMapp.

The drug is composed of three antibodies that bind to Ebola. The immune system then identifies the infected cells, and attacks them.

ZMapp was given to Dr Kent Brantly and Nancy Writebol – American humanitarian workers who were treating Ebola patients in Liberia and became infected themselves. Both health care workers were medically evacuated from Africa to Emory University Hospital in Atlanta, Georgia. Since their arrival, Dr Brantly was reported to be steadily improving, and Writebol is in a stable condition.

Meanwhile, 163 new cases of Ebola infection and 61 deaths were reported in just two days by the World Health Organisation, and 932 deaths have been attributed to the outbreak since February. The West African countries of Guinea, Liberia, and Sierra Leone have been devastated by the virus.

Liberian Assistant Health Minister Dr Todd Nyenswah said that his office has been inundated with requests from family members of Ebola-infected persons asking for ZMapp.

"This is something that has made our job most difficult," Dr Nyenswah told the Wall Street Journal. "The population here is asking, 'You said there was no cure for Ebola, but the Americans are curing it?'"

President Obama met with African leaders on Wednesday, and said that the best defense against Ebola is prevention, education, and containment.

"We've got to let the science guide us," he said. "I don't think all the information is in on whether this drug is helpful. What we do know is that the Ebola virus - both currently and in the past - is controllable if you have strong public health infrastructure in place.

"Let's get all the health workers that we need on the ground. Let's help to bolster the systems that they already have in place."

Those recommendations were echoed by Centers for Disease Control and Prevention (CDC) Director Tom Frieden, who also added that there are "virtually no doses" of ZMapp available.

"The bottom line with Ebola is we know how to stop it: traditional public health," he told the Associated Press on Wednesday. "Finding and isolating patients, finding and educating who's been in contact with them and strict hospital infection control."