NEW YORK - Aides to President Barack Obama Sunday criticized decisions by three US states to quarantine people who are returning from Ebola-stricken West Africa.

New York, New Jersey and Illinois imposed 21-day mandatory quarantines in the last two days for anyone arriving with a risk of having contracted Ebola in Sierra Leone, Liberia and Guinea. They are the three West African countries that have borne the brunt of an epidemic that has killed nearly 5,000 people.

But critics worry the policies, going beyond federal regulations and intended to ease public concern over the spread of the disease, will just make matters worse.

Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, and US Ambassador to the United Nations Samantha Power said quarantines may discourage health workers from traveling to West Africa to help block the disease at its source.

"If you put everyone in one basket, even people who are clearly no threat, then we have the problem of the disincentive of people that we need," Fauci said on ABC's This Week. "Let's not forget the best way to stop this epidemic and protect America is to stop it in Africa, and you can really help stopping it in Africa if we have our people, our heroes, the health care workers, go there and help us to protect America." Fauci reiterated what the medical officials have been stressing as Americans worry about Ebola: that it is spread only by contact with bodily fluids of people with symptoms. "The science tells us that people who are not sick, if you do not come into contact with body fluid, if someone comes back from wherever, Liberia, and they're well, they are no danger to anyone," Fauci said.

Ms. Power, who is traveling in West Africa, told NBC News that quarantine plans in New York, New Jersey and Illinois are "haphazard and not well thought out," and could discourage health workers from going to West Africa in the first place.

"We cannot take measures here that are going to impact our ability to flood the zone," Ambassador Power said. "We have to find the right balance between addressing the legitimate fears that people have and encouraging and incentivizing these heroes."

Officials in New Jersey, New York and Illinois, who acted in the wake of a new Ebola case in New York, said they cannot rely on people to quarantine themselves.

"I don't think when you're dealing with something as serious as this you can count on voluntary system," said New Jersey Gov. Chris Christie, a Republican, speaking on Fox News Sunday. "This is the government's job."

He added: "I think this is a policy that will become a national policy sooner or later."

Republican members of Congress have also called on the Obama administration to enact more travel restrictions into and out of West Africa.

Congressman Darrell Issa, a Republican, , chairman of the House Oversight and Government Reform Committee, told CNN's State of the Union that state officials are taking action in the absence of federal leadership.

"Governors of both parties are reacting because there isn't a trust in the leadership of this administration," Issa said.

A nurse who returned on Friday through New Jersey's Newark airport after working in Sierra Leone with Ebola patients, strongly criticized the quarantine policy on Saturday, describing hours of questioning and then transfer to a hospital isolation tent. She called her treatment a "frenzy of disorganization."

The quarantine measures were imposed in part in response to the new case in New York - Dr. Craig Spencer, who was diagnosed on Thursday after working with Ebola patients in Guinea. Many New Yorkers were worried when it emerged he had been out and about in the city between coming home and developing symptoms.

Both he and Kaci Hickox, the nurse who was quarantined after coming home from Sierra Leone on Friday, worked with Doctors Without Borders, the medical charity that has been a leading part of international efforts to fight the epidemic in West Africa.

The charity has criticized the treatment of Hickox in Newark and questioned the quarantine policies on Sunday.

"Quarantine measures or coercive measures against aid workers could give a superfluous sense of security, while the most important (thing) is to tackle the epidemic at its source," Sophie Delauney, the charity's executive director in the United States, said on "Meet the Press."

Hickox said after her experience that she feared for what lies ahead for other U.S. health workers trying to help combat the epidemic. "Will they be made to feel like criminals and prisoners?" she wrote in an article published on Saturday by The Dallas Morning News on its website.

Newark's University Hospital said the nurse remained in isolation and under observation on Sunday "in a climate-controlled, indoor, extended care area in a building adjacent to the hospital."

Ebola has killed almost half of more than 10,000 people diagnosed with the disease - predominantly in Liberia, Sierra Leone and Guinea - although the true toll is far higher, according to the World Health Organization.