Secretary of state John Kerry has indicated that five Guantánamo Bay detainees released in exchange for an American soldier could be killed by drone strike if they return to the battlefield in Afghanistan.

Kerry’s implied threat to the five Taliban fighters came as Republicans ramped-up their criticism of the deal to release Sergeant Bowe Bergdahl, a prisoner of the Taliban for five years until he was freed last week.

The 28-year-old soldier has reportedly told medical staff at a base in Germany he was tortured and beaten by his captors, and once locked in a metal cage in total darkness as punishment for an attempted escape.

On Sunday, it emerged that the FBI is investigating death threats against Bergdahl’s parents, who have not reacted publicly to the intense political debate raging over the wisdom of trading five Guantánamo detainees for their son.

Republicans highlight the possibility that the Taliban fighters, some of whom were senior commanders, are likely to return to the Afghan conflict after the year they are compelled to stay in Qatar, which brokered the prisoner swap and has promised to monitor the five men.

However, Kerry told CNN the men were also being closed monitored by the US, which had "the ability to do things" if the terms of the arrangement with Qatar were violated. Although he did not overtly refer to drone strikes, he said the five men would be liable to be killed by the US if they returned to the ranks of the Taliban.

“I am not telling you they don’t have the ability to go back and get involved [in the Afghan conflict],” he said. “But they also have an ability to get killed doing that. I don’t think anybody should doubt the capacity of the United States of America to protect Americans.”



Asked if that meant the US would kill the men, Kerry replied: “The president has always said he will do whatever is necessary in order to protect the United States of America … so these guys pick a fight with us in the future, now, or at any time, at enormous risk. We have proven what we are capable of doing with the core al-Qaida in west Pakistan, Afghanistan.”



The CIA is believed to have conducted more than 350 drone strikes in Pakistan since 2004, killing hundreds of al-Qaida-aligned fighters.

Republican senators criticise deal for Bergdahl. Guardian

Kerry added that it would have been “offensive and incomprehensible” to leave Bergdahl in Afghanistan, where Obama is quickly winding down the US military presence – a process he recently said would be complete by the end of 2016.

“To leave an American behind in the hands of people who would torture him, cut off his head, do any number of things – we would consciously choose to do that?” Kerry asked.

However many Republicans, and some Democrats, have said the prisoner swap has placed a bounty on the heads of Americans in the region, including diplomats and staff of independent non-governmental organisations.

Others argue that Bergdahl, who has been called a deserter by some former members of his platoon, for apparently walking off his base in the lead-up to his capture, did not deserve to be rescued at such a high cost.

It remains unknown why in 2009 Bergdahl left his remote military outpost, near the border with Pakistan, unarmed. Military psychologists caring for the soldier in Germany have not begun the process of fully debriefing him. The US army has promised an inquiry into his disappearance from base, and urged the public not to jump to conclusions.



Although his psychological assessments are at an early stage, the New York Times reported that Bergdahl told medical officials the Taliban locked him in a metal cage in total darkness for weeks at a time, as retribution for an attempted escape.



The soldier was said to be suffering from skin and gum disorders associated with poor hygiene. He was also reportedly refusing to be addressed as "sergeant" – a title he acquired as a result of two promotions while in captivity.



Senator John McCain, himself a former PoW and now a critic of the Obama administration over the Bergdahl deal, previously indicated support for prisoner swaps. Photograph: Maciej Kulczynski/EPA Photograph: MACIEJ KULCZYNSKI/EPA

The Associated Press reported a similar account, adding that Bergdahl said he had been “tortured”. Both media organisations, citing unnamed US officials, said the soldier was physically well enough to travel but required further psychological assistance before being transferred to another military medical centre in San Antonio, Texas, where he is likely to be reunited with his family.

Both the White House and Department of Defense declined to comment on the reports.

Rear Admiral John Kirby, the Pentagon press secretary, issued a statement on Sunday that said: “The Department of Defense does not comment on discussions that Sergeant Bergdahl is having with the professionals who are providing him

medical and reintegration care. We will respect that process in all regards.

"As we have noted, the army will conduct a comprehensive review to learn the circumstances of Sergeant Bergdahl's disappearance and captivity. That process, too, needs to be respected.



"Our focus remains on providing him with the care he needs."



The military’s top brass have publicly stood by the decision to trade the Guantánamo inmates for Bergdahl. One exception is a retired lieutenant general, Jerry Boykin, who on Sunday said Bergdahl’s alleged crime of desertion could be “punishable by death” in a time of war – a factor he said should have been considered when weighing the deal.

“We have traded for a guy who is guilty of a crime that is actually punishable by death,” he said. “We traded him for five of the worst Taliban leaders in Guantánamo, two of which are mass murderers, all of which [could] be back on the battlefield, and all of which will be threats not only to Americans but to the Afghan people.”

The Arizona senator John McCain, one of several Republicans who a few months ago were voicing support for the idea of a Guantánamo prisoner swap in exchange for Bergdahl’s release and are now leading the charge against Obama’s decision, also focused on the threat posed by the Taliban fighters.



“What we’re doing here is reconstituting the Taliban government – the same guys that are mass murderers, one killed thousands of Shiite Muslims,” he told CNN.

“These are the people who used to take women into the soccer stadium in Kabul and hang them from the goalposts.”

He added: “I think we should do everything we can in our power to win the release of any American being held, but not at the expense of the lives and wellbeing of their fellow service men and women.”

McCain said his view would be the same had Bergdahl been captured by the Taliban in battle, rather than after having left his post.



But Bergdahl’s perceived disloyalty – allegedly abandoning his fellow soldiers after growing disillusioned with the US war effort – has been a central thrust to Republican criticism over the prisoner swap. There has also been condemnation of his father, Bob Bergdahl, a critic of the war in Afghanistan.

Bob Bergdahl speaks to the Guardian, before the release of his son. Guardian

Bob Bergdahl surprised White House officials eight days ago when, appearing alongside Obama at a Rose Garden press conference to announce his son's release, he made a few remarks in Pashto and Arabic. That was considered a White House PR failure, and critics have said Obama should not have appeared alongside the soldier's father, who has been mocked for his long, “Taliban-style” beard.

Since then Bob Bergdahl and his wife, Jani, have been the recipients of death threats, which the FBI said over the weekend it was taking seriously. A welcome-home party for Bergdahl in his family’s hometown of Hailey, Idaho, was cancelled.

James Mattis, a retired marine corps general who has worked closely with Bergdahl's parents and has supported them over the last week, said they were “keeping their balance” in the face of the threats.



“These are two salt of the earth people,” he said. “They’re regular old Americans. I think most of us got over judging people by the length of their hair about 1975 in this country.

“I think a certain amount of compassion is appropriate for a family that has been through this.”

