– The Centers for Disease Control and Prevention on Wednesday placed its emergency operations center in Atlanta on the highest response level because of the worsening Ebola outbreak in West Africa.

The move came as more cases of the deadly virus migrated from rural villages and towns in Guinea, ­Liberia and Sierra Leone to urban areas in Nigeria, where it could spread more quickly.

The number of Ebola deaths in the region has reached 932, according to the World Health Organization, while the number of confirmed or suspected cases has now reached 1,711.

The World Health Organization is debating whether the outbreak constitutes a "public health emergency of international concern." If so, WHO will recommend temporary measures to reduce the international spread of the disease.

Next week, WHO will convene a panel of medical ethicists to explore using experimental treatments for Ebola patients in West Africa. Ebola only spreads through contact with infected bodily fluids.

While no vaccine is available, several are being developed. They include ZMapp, an experimental immune system booster. Two Americans who had been working with patients in West Africa and were stricken with Ebola are hospitalized at Emory University Hospital in Atlanta and reportedly have been treated with ZMapp, even though the drug has never been tested on humans.

President Obama told reporters Wednesday that the United States would not send supplies of ZMapp to the epicenter of the outbreak in West Africa because it's unclear whether the drug is actually helpful. It's also "premature," Obama said, to discuss fast tracking the approval process for Ebola drugs.

"We are in an unusual situation in this outbreak," said Dr. Marie-Paule Kieny, WHO assistant director-general. "We have a disease with a high fatality rate without any proven treatment or vaccine. We need to ask the medical ethicists to give us guidance."

Obama said the outbreak continues to grow, in part because the affected countries have weak public health systems that have been overwhelmed by the challenge of quickly identifying and isolating Ebola patients.

In addition, distrust of public health workers by local villagers has also hampered response efforts, he said.

"As a consequence, it spread more rapidly than has been typical with the periodic Ebola outbreaks that have occurred previously," Obama said.

While the United States must take the crisis seriously, Obama said, Ebola can be "controlled and contained very effectively if we use the right protocols."

As the United States and other international players continue to provide public health assistance in West Africa, Obama said it may become "entirely appropriate to see if additional drugs or medical treatments" can improve survival rates.

The CDC is sending 50 additional disease control experts to the four affected African nations to help treat patients and contain the disease.