Some people in affected countries already have wondered why the drug wasn't offered to any infected people in Africa. Dr. Anthony Fauci of the National Institutes of Health said the manufacturer has told the U.S. government that it would take two to three months to produce even "a modest amount."
"We don't even know if it works," he stressed.
President Barack Obama, who hosted an Africa summit this week, pledged to help "nip as early as possible any additional outbreaks of the disease.
"And then during the course of that process, I think it's entirely appropriate for us to see if there are additional drugs or medical treatments that can improve the survivability of what is a very deadly and obviously brutal disease, Obama said Wednesday.
Underscoring desperate attempts to stop the disease, which has killed almost 1,000 people since March, troops deployed to block people traveling to Liberia's capital Thursday from rural areas hit by Ebola. President Ellen Johnson Sirleaf declared a national state of emergency, and officials said Thursday that no one with a fever would be allowed in or out of the country.
In neighboring Sierra Leone, military forces also deployed as part of "Operation Octopus" which officials said was aimed at preventing "the unauthorized movement of Ebola-infected persons."
While the outbreak has now reached four countries across West Africa, Liberia and Sierra Leone account for more than 60 percent of the deaths, according to the World Health Organization. The outbreak that emerged in March has claimed at least 932 lives.
"This outbreak, because of its size and its geographical extent, certainly merits an extraordinary response and we know countries have announced they must take extraordinary measures, so that is understandable from a public health perspective," said WHO spokesman Gregory Hartl in Geneva.
Liberian Information Minister Lewis Brown vowed stringent surveillance at the country's international airport where many flights have been cancelled because of the outbreak.
"We are facing a threat of the greatest proportion," Brown said. "No one, absolutely no one will be allowed to enter or leave our country with temperature above normal."
The unprecedented measures came after a man sick with Ebola in Liberia boarded a flight and ended up in Nigeria, Africa's most populous nation, where a nurse who treated him is now dead from the disease and several other people are infected. The traveler also died.
Ebola is spread only through direct contact with the bodily fluids of people showing symptoms which include a fever, body aches and vomiting and progresses to internal and external bleeding.
Experts warned that extreme measures risk driving patients and their families further underground out of fear. The best way to track possible exposures is through community leaders who are known and respected, they say.
"Nothing replaces that sense of community trust. So if you come in with brute force, things might appear to be working but it could be pushing people out where they can't control the borders and the disease gets out," said Dr. David Heymann, professor at London School of Hygiene and Tropical Medicine.
Sirleaf justified the 90-day state of emergency, saying the outbreak requires "extraordinary measures for the very survival of our state and for the protection of the lives of our people."
"Ignorance, poverty, as well as entrenched religious and cultural practices continue to exacerbate the spread of the disease especially in the counties," Sirleaf said late Wednesday.
She warned that some civil liberties could be suspended as needed, and by Thursday soldiers already were restricting movements on the roads to Monrovia, witnesses said. Some soldiers were deployed to the crossroads town of Klay about 25 miles (40 kilometers) west of Monrovia in an effort to stop people from three Ebola-infected counties from coming closer to the capital.
Yet even as authorities tried to keep more people from reaching Monrovia, the capital already has been hit by the virus, with bodies abandoned in the streets. Relatives are hiding feverish patients at home for fear if they are brought to isolation centers and don't have Ebola they will end up contracting it anyway.
National Health Workers Association president Joseph Tamba said the state of emergency is necessary. But he says people should have been given advance notice to buy food ahead of the movement restrictions.
In Sierra Leone, President Ernest Bai Koroma mandated that all Ebola victims must now be buried near where they died to minimize exposure while transporting highly contagious corpses.
"All such burials should be reported to the Ministry of Health and Sanitation, which will give necessary clearance," the order stated. "Death certificates must be issued before burials."
In other developments:
A Spanish missionary infected by Ebola was in stable condition after being flown to Spain from Liberia Thursday, health officials in Madrid said. Miguel Pajares, 75, had been helping to treat people infected with Ebola and was one of three who tested positive at the San Jose de Monrovia Hospital in Liberia earlier this week.
Zimbabwe President Mugabe is considering withdrawing Zimbabwean soldiers, police and prison officers serving as U.N. peacekeepers in Liberia because of the Ebola outbreak, Zimbabwe's state-run Herald newspaper reported. "We must not expose ourselves unnecessarily," Mugabe was quoted as saying. Peacekeepers from dozens of countries were deployed in Liberia at the height of peacekeeping operations in a country that was riven by two civil wars. They are to remain until elections in 2017.
Associated Press writers Maria Cheng in London and Clarence Roy-Macaulay in Freetown, Sierra Leone contributed to this report.