WASHINGTON -- Secretary of State John Kerry said Sunday that he is confident the five Taliban detainees freed in a swap for Sgt. Bowe Bergdahl posed little risk to Americans, adding that Qatari officials were not the only ones monitoring them.

He also said that while the five might be able to return to the battlefield, "they also have the ability to get killed doing that."

Kerry, in some of his first public remarks on the exchange, struck a tough tone, dismissing as "baloney" the suggestion that terrorists would have new incentive to kidnap Americans. He also hinted, without offering details, that the United States had the means to monitor the Taliban members, who are now in Qatar, and act against them if necessary.

The Qataris "aren't the only ones keeping an eye on them," Kerry said on the CNN's State of the Union. He added, "These guys pick a fight with us in the future or now or at any time at enormous risk."

"No one should doubt the capacity of America to protect Americans," Kerry said. "We have proven what we are capable of doing with al-Qaida."

Bergdahl, held captive for almost five years, was released May 31 in exchange for five Taliban prisoners held by the U.S. at the Guantanamo Bay prison camp in Cuba. The deal requires that the five men remain in Qatar for at least a year.

The threats by the Taliban prisoners to resume fighting in Afghanistan and kill Americans amount to propaganda, Kerry said.

"They'll say whatever they want to stir the waters," he said.

Broadly defending the swap, Kerry said that it would have been "offensive and incomprehensible" to leave Bergdahl in the hands of people who might torture him or "cut off his head."

Despite the defense of administration decisions by officials like Kerry, the criticism over the exchange continued Sunday, with Republican lawmakers and one senior Democrat publicly expressing fresh doubts.

Sen. John McCain, an Arizona Republican and former Vietnam prisoner of war, criticized the deal on State of the Union.

The five Taliban prisoners "were evaluated and judged as too great a risk to release," McCain said. "I'm sad to tell you I'm afraid they're going to re-enter the fight."

The administration received key support, however, from an influential retired military leader, Gen. James Mattis, who said that the exchange would make it easier now to attack the extremist groups involved in Bergdahl's detention.

Up to now, the general said, every time commanders weighed an attack on the Haqqani Network, which operates on both sides of the Afghanistan-Pakistan border, "we were concerned that Bowe Bergdahl could end up dead."

That concern is gone, he said on CNN.

"There's also a freedom to operate against them that perhaps we didn't fully enjoy," he said.

Mattis -- who headed the U.S. Central Command from 2010 to 2013, with responsibility for Afghanistan -- also argued that the Qataris, with "some of their own prestige at stake," had reason to monitor the Taliban officials closely.

Like Kerry, the general dismissed the idea that the swap might inspire terror groups to kidnap Americans, saying, "It's not like all of a sudden they have a new impulse here."

With the U.S. combat role in Afghanistan coming to an end and most troops to be withdrawn by the end of 2016, opportunities for Taliban to kidnap Americans will dwindle, Kerry said.

Key members of Congress have expressed serious concerns that the administration failed to inform them in advance of the Bergdahl exchange.

On Sunday, the leaders of the intelligence committees in both chambers, Sen. Dianne Feinstein of California and Rep. Mike Rogers of Michigan, raised the question of why the administration had backed away from a goal enunciated in 2011: to make the Bergdahl deal the first step in a broader, behind-the-scenes effort to reach a reconciliation agreement with the Taliban.

Feinstein, a Democrat, also said that she found it hard to accept Kerry's assurances that the Taliban members could be kept securely in Doha, the capital of Qatar. Previous negotiations, she said, had included a requirement for the house arrest of the five, in contrast to the current arrangement, which reportedly will allow them to move about the country.

"You can't help but worry about them in Doha," she said on CBS' Face the Nation. "And we have no information on how the United States is actually going to see that they remain in Doha, that they make no comments, that they do no agitation.

"It's hard to be comfortable when you really haven't been briefed on the intricacies of carrying out this agreement."

Bergdahl, who remains at an Army medical center in Landstuhl, Germany, has told medical officials that his former captors locked him in a metal cage in darkness for weeks at a time as punishment for trying to escape. A U.S. defense official declined to confirm that account.

Feinstein said she had heard rumors of Bergdahl trying to escape his captivity, though she said she had never heard of any allegations of torture.

Rogers, a Republican, said that he was convinced that at least three of the Taliban members, and perhaps all five, would try to return to the battlefield. In the meantime, he said on ABC's This Week, they can meet in Qatar with other Taliban figures, or with visiting family members, and send messages by courier to Afghanistan or Pakistan.

Rogers said he did not expect the five to plan anything "operational," that is, to plan attacks. But he said the conditions of their time in Qatar would allow them "to prepare for what's next."

Information for this article was contributed by Brian Knowlton of The New York Times and by David Lerman and Greg Giroux of Bloomberg News.

A Section on 06/09/2014