UNITED NATIONS, Aug. 7 -- The World Health Organization (WHO) will convene a panel of experts in medical ethics early next week to explore the use of experimental treatment in the ongoing Ebola outbreak in West Africa, a UN spokesman said here Thursday.

"Currently there is no registered medicine or vaccine against the virus, but there are several experimental options under development," Farhan Haq, the deputy UN spokesman, said at a daily news briefing here.

"The World Health Organization notes that the recent treatment of two health workers with experimental medicine has raised questions," Haq said. "It stresses that the gold standard for assessing new medicine involves a series of trials in humans, and that the guiding principle with use of any new medicine is 'do no harm'."

"However, Dr. Marie-Paule Kieny, assistant director-general at the World Health Organization, explained that the current situation was unusual and that guidance from medical ethicists was needed," he added.

As a "secret serum" called ZMapp emerged as the primary treatment of two American aid workers infected with Ebola in West Africa, experts warned that it is too early to tell if the treatment is effective.

International attention has turned to the experimental drug known as ZMapp, developed by San Diego-based Mapp Biopharmaceutical and manufactured by Owensboro-based Kentucky BioProcessing (KBP), because Nancy Writebol and Kent Brantly, who contracted the deadly disease while treating patients in Liberia, seemed to be improving after they were treated with the medication.

The U.S. manufacturer of the first alleged treatment confirmed on Wednesday it provided "a limited amount of ZMapp" to Emory University Hospital in Atlanta, where the two are being treated, after it received a request last week from the hospital and the Samaritan's Purse, a Christian aid organization Brantly worked for.

West African countries hard-hit by the Ebola virus have issued travel restrictions in an effort to contain the spread of the deadly disease after reports emerged of families hiding sick relatives and abandoning bodies in the streets.

On Wednesday, the Nigerian government described the Ebola outbreak in the country as a national emergency.

Soldiers clamped down on people trying to travel to Liberia's capital on Thursday from rural areas with high rates of Ebola infection, hours after the president declared a national state of emergency.

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.

The outbreak, by far the largest in the nearly 40-year history of the disease, has infected 1,711 people and killed 932 this year in four western African countries -- Guinea, Liberia, Nigeria and Sierra Leone -- according to the WHO.

While the outbreak, which emerged in March, has now reached the four countries, Liberia and Sierra Leone account for more than 60 percent of the deaths, according to the WHO.