Similar efforts were underway in eastern areas of neighboring Sierra Leone after officials there launched "Operation Octopus" to try to keep those sick with Ebola in isolation.

While the outbreak has now reached four countries, 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.

Two American aid workers who caught the virus in Liberia are being treated in the United States, one Saudi national being tested for the virus died on Wednesday in Saudi Arabia, and a Spanish missionary infected with Ebola is being treated in Spain — raising global fears that the virus could possibly spread outside Africa. Still, officials have said Ebola is controllable in countries with strong public health infrastructure. The virus has spread fastest in rural areas of West Africa, largely due to the lack of such infrastructure.

"Ignorance, poverty, as well as entrenched religious and cultural practices continue to exacerbate the spread of the disease especially in the counties," Liberian President Ellen Johnson Sirleaf said late on Wednesday as she announced a 90-day state of emergency.

Sirleaf said this Ebola outbreak, the worst recorded in history, requires "extraordinary measures for the very survival of our state and for the protection of the lives of our people." She warned that some civil liberties could be suspended as needed, and by Thursday soldiers were already restricting movements on the roads to the capital, Monrovia, witnesses said.

Some soldiers were deployed to the crossroads town of Klay about 25 miles west of Monrovia in an effort to stop people from three Ebola-infected counties from coming closer to the capital. Even though authorities are trying to keep more people from reaching Monrovia, the capital has already seen people infected with the virus.

National Health Workers Association President Joseph Tamba said the state of emergency is necessary, but that people should have been given advance notice to buy food ahead of the movement restrictions.

There is no known cure for Ebola, a hemorrhagic fever that has overwhelmed rudimentary health care systems in West Africa, but an experimental treatment, called ZMapp, is currently being assessed — and has been used on the two Americans being treated in Atlanta. Both patients seem to be showing signs of improvement.

But U.S. President Barack Obama said on Wednesday that it was too early to use the experimental treatment in West Africa.

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

Nevertheless, Canadian drugmaker Tekmira Pharmaceuticals said Thursday that the U.S. Food and Drug Administration modified a hold recently placed on a different experimental drug, TKM-Ebola, which targets the genetic material of Ebola.

Tekmira said the agency "verbally confirmed" changes to the hold that may allow the company to make the drug available, although it has yet to be proven as safe and effective.

The World Health Organization said on Wednesday that it would ask medical ethics experts to explore emergency use of experimental treatments in West Africa.

Al Jazeera and wire services