WASHINGTON - The new U.S. Ebola "czar" starts work on Wednesday and a military medical team begins training as the Obama administration ramps up its response to the potential spread of the virus in the United States.

The Pentagon's 30-member emergency team, including 5 doctors, 20 critical care nurses and 5 trainers who are experts in infectious disease protocols, were scheduled to gather at Fort Sam Houston in San Antonio, Texas.

U.S. Defense Secretary Chuck Hagel ordered the creation of the rapid-response team to support civilian medical personnel after three people were infected in the United States with the virus that has killed more than 4,500 people, mostly in West Africa.

U.S. President Barack Obama was scheduled to hold a meeting on Wednesday with Ron Klain, his new Ebola response coordinator, amid rising Republican criticism ahead of congressional elections next month.

The administration has ratcheted up its response but has so far stopped short of a travel ban from West Africa, demanded by some lawmakers.

The Department of Homeland Security said on Tuesday that travelers from three countries at the center of the epidemic would be funneled to one of five major U.S. airports conducting enhanced screening for the virus. Restrictions on passengers whose trips originated in Liberia, Sierra Leone or Guinea were due to go into effect on Wednesday.

Affected travelers will have their temperatures checked for signs of a fever that may indicate Ebola infection, among other protocols, at New York's John F. Kennedy, New Jersey's Newark, Washington Dulles, Hartsfield-Jackson Atlanta, and Chicago's O'Hare International airports, officials said.

"We are working closely with the airlines to implement these restrictions with minimal travel disruption," Homeland Security Secretary Jeh Johnson said in a statement. "If not already handled by the airlines, the few impacted travelers should contact the airlines for rebooking, as needed."

A Reuters/Ipsos online poll released on Tuesday showed that nearly three-fourths of 1,602 Americans surveyed favored a U.S. ban on civilian air travel in and out of Liberia, Sierra Leone and Guinea.

White House spokesman Josh Earnest told reporters that Obama is "not philosophically opposed to a travel ban" on West Africa, and remains "open to it" if the scientists and public health experts advising him say it would help protect Americans. Earnest said the advisers currently oppose such a ban.

The only three cases diagnosed in the United States all occurred in Texas; Liberian Thomas Eric Duncan, who died on Oct. 8 in Dallas, and two nurses who treated him.

On Tuesday, the U.S. National Institutes of Health (NIH) outside Washington, D.C., upgraded the medical condition of one of the nurses, Nina Pham, to good from fair. She entered a special NIH facility in Bethesda, Maryland, for treatment last Thursday.

The other nurse, Amber Vinson, is being treated at Emory University Hospital in Atlanta. Vinson's mother has said her daughter is weak but recovering.

NBC freelance cameraman Ashoka Mukpo, an American who contracted Ebola while working in West Africa, is free of the virus and will leave the Nebraska Medical Center on Wednesday, the hospital said. Mukpo arrived in the United States on Oct. 6 for treatment.