WASHINGTON — In often chilling testimony Thursday, an official with a relief organization responding to the Ebola crisis in West Africa labeled efforts to control the virus a failure.

Ken Isaacs, a vice president with Samaritan’s Purse, a North Carolina-based Christian humanitarian organization, also said the number of Ebola cases and deaths reported by the World Health Organization (WHO) are probably 25 percent to 50 percent below actual levels.

During testimony before a subcommittee of the House Committee on Foreign Affairs, Isaacs said volunteers in the affected countries were in dire need of enhanced international support, including aircraft equipped to transport Ebola patients, more laboratories to speed the processing of blood tests and more security for health workers who face violence and a lack of cooperation from villagers.

Isaacs told of a prominent Liberian doctor who “openly mocked the existence of Ebola” by trying to enter a hospital isolation ward with no gloves or protective clothing. He and another man who accompanied him to the hospital died within five days, Isaacs said.

Before the current outbreak, Ebola had collectively stricken 2,232 people and killed 1,503 people in 32 years, Isaacs testified. “Easily this present outbreak is going to surpass that in fatalities, as well as overall cases,” he said. “It is clear to say that the disease is uncontained and it is out of control in West Africa. The international response to the disease has been a failure and it is important to understand that.”

He added: “It was not until July 26 when Kent Brantly and Nancy Writebol were confirmed positive that the world sat up and paid attention.”

Writebol, 59, a missionary from Charlotte, N.C., and Brantly, 33, of Fort Worth, Texas, are in Emory University Hospital in Atlanta after contracting Ebola while treating patients in Liberia. Both were part of a missionary response team sponsored by Samaritan’s Purse and another relief organization, SIM USA.

As of Thursday, WHO reported that the Ebola crisis ravaging Guinea, Liberia, Sierra Leone and now Nigeria had killed 932 people, with 1,711 confirmed and suspected cases.

Ebola only spreads through contact with infected bodily fluids. It cannot be transmitted through airborne particles. It has a death rate of roughly 45 to 90 percent.

In earlier testimony, U.S. Centers for Disease Control and Prevention (CDC) Director Tom Frieden didn’t rule out the possibility that a traveler could arrive in the U.S. unknowingly infected with Ebola. But he said he is confident there will not be a large Ebola outbreak here.

Nigeria has requested access to the experimental drug ZMapp, used on Writebol and Brantly. “The plain fact is that we don’t know whether that treatment is helpful,” Frieden said. He added, “I don’t want any false hopes out there.”

On Thursday, the Food and Drug Administration did modify a clinical hold on an experimental Ebola drug made by Tekmira Pharmaceuticals of Canada. That allows potential use of the drug, TKM-Ebola, on people infected with the virus.

Material from The Associated Press is included in this report.