As the death toll from the Ebola outbreak in four West African nations officially climbed above 1,000, the World Health Organization on Tuesday said the use of unproven, experimental treatments and vaccines is ethical given the magnitude of the crisis.

Marie-Paule Kieny, assistant WHO director general, said she hopes that efforts to produce more of an Ebola treatment developed by a small San Diego biopharmaceutical company, as well as other drugs under development, could result in wider availability late this year or early in 2015. There currently is no vaccine or cure for Ebola, but several treatments are in various stages of clinical development.

The San Diego company, Mapp Pharmaceutical, has said that the remaining supply of its ZMapp treatment, which was used on two U.S. missionaries who contracted the Ebola virus, was exhausted after it sent several doses to Liberia. The Liberian government said Tuesday it would give ZMapp to two doctors, Zukunis Ireland and Abraham Borbor, who had fallen ill with the virus while treating patients.

A panel of experts convened by the WHO this week agreed that the use of experimental treatments for the disease is ethical, but the agency’s declaration Tuesday did not address the difficult questions about who should receive the limited amount of drugs available.

The shortage of medications amounts to “a market failure,” Kieny said. “It’s a market failure because this is typically a disease of poor people in poor countries, and so there is no market.” As a result, she said, “there are no clinical stockpiles” and the best authorities can do is “accelerate development and scale up” as quickly as possible. Kieny said the WHO will convene another panel at the end of August to discuss prioritizing distribution of scarce medications.

The two American patients who were sickened while treating the outbreak in Liberia both received ZMapp, which had never been tested in humans. Both are improving after being flown to the United States for treatment in an Atlanta hospital. But a Spanish priest who reportedly was also given the drug died Tuesday, according to media reports.

The WHO said Tuesday that the death toll from Ebola in Guinea, Sierra Leone, Liberia and Nigeria had reached 1,013. A total of 1,848 cases have been reported.

Several other African nations are closely monitoring ill patients suspected to have contracted the disease. Aside from Guinea, Liberia and Sierra Leone — the three countries where the outbreak initially spread — only Nigeria, Africa’s most populous country, has confirmed cases of Ebola. Nigeria has confirmed 10 cases, and two of the patients have died.

Still, fear over the spread of the virus has continued to cripple West Africa. In Liberia, aid workers fear they are losing the battle with the virus as the country’s frail medical system is stretched beyond its limits. The situation is “catastrophic,” Lindis Hurum, Doctors Without Borders’ emergency coordinator in Liberia, said in a recent statement. The organization has more than 600 doctors working in the region but says that more are desperately needed.

As the outbreak worsens, U.S. officials have said they intend to fast-track development of an Ebola vaccine and could begin human trials next month. The potential vaccine has shown encouraging results in non-human primates, and if human testing goes well it could be available in limited amounts next year.

At the same time, the Food and Drug Administration has said it continues to work with other federal agencies, such as the National Institutes of Health, to fund the development of Ebola drugs and to speed up treatments already in the pipeline. Last week, the FDA said it had removed one regulatory hurdle for an Ebola drug under development by a Canadian company, Tekmira. The move would allow the potential use of the drug for Ebola victims in the near term.

Brady Dennis contributed to this report.

The Ebola epidemic over time