An ethics meet to explore the use of experimental treatment in the Ebola outbreak in West Africa was called for by WHO, they said on Wednesday.
The move comes after two health workers from the US charity Samaritan's Purse were treated with medication that the WHO said had never been tested and shown to be safe in people.
"We are in an unusual situation in this outbreak. We have a disease with a high fatality rate without any proven treatment or vaccine," said Marie-Paule Kieny, assistant director-general of the UN health agency.
Samaritan's Purse members Kent Brantly and Nancy Writebol were stricken with Ebola while treating patients in Liberia.
The patients, who were rushed to the United States amid tight medical security, were reportedly given an experimental drug known as ZMapp.
Both have shown improvements in their health and are now being treated in isolation at an Atlanta, Georgia hospital.
There is currently no registered medicine or vaccine against the Ebola virus -- which in the past has shown fatality rates approaching 90 percent -- but there are several experimental options under development.
The WHO said experimental drugs raised questions about whether they should be deployed during such an outbreak and, given the extremely limited amount available, who should receive them if they were used.
"The gold standard for assessing new medicine involves a series of trials in humans, starting small to make sure the medicine is safe to use. Then, the studies are expanded to more people to see how effective it is, and how best to use it," said the WHO.
"The guiding principal with use of any new medicine is 'do no harm'. Safety is always the main concern," it added.
The Ebola virus causes fever, vomiting, diarrhoea, muscle aches and sometimes organ failure and hemorrhaging.
The ongoing outbreak in West Africa is the deadliest in history, having killed 932 of the more than 1,700 infected.