US army chief Dempsey: Bowe Bergdahl could be prosecuted
The top-ranking US military officer has raised the possibility Sgt Bowe Bergdahl could be prosecuted if he abandoned his post before his capture.
Gen Martin Dempsey said the Army would not ignore misconduct but the 28-year-old was "innocent until proven guilty".
The US Army later confirmed it will launch a new review into the circumstances surrounding Sgt Bergdahl's capture.
He was released on Saturday after five years in Taliban captivity.
US President Barack Obama has defended the decision to free five senior Taliban leaders as part of the deal, amid criticism it puts lives at risk.
Addressing the accusation from Sgt Bergdahl's fellow soldiers that he deserted his post before capture, Mr Obama said the US had a "pretty sacred rule" not to leave soldiers behind.
"We don't leave our men or women in uniform behind and that dates back to the earliest days," Mr Obama said at a news conference in Warsaw.
"Regardless of the circumstances, whatever those circumstances may turn out to be, we still get an American soldier back if he's held in captivity. Period. Full stop. We don't condition that."
Since Sgt Bergdahl's release on Saturday, a growing chorus of opposition Republicans have criticised the president's decision to order the prisoner swap.
They have attacked the president for undertaking what they describe as negotiations with terrorists, and say the transfer of five Taliban senior prisoners from the detention facility at Guantanamo Bay, Cuba, to Qatar, puts Americans at risk.
And some have accused the president of contravening a law requiring the White House to notify Congress 30 days in advance of any transfers of prisoners from Guantanamo.
Dianne Feinstein, the Democratic chairman of the Senate Select committee on Intelligence said she and other senior committee members had received an apology from the White House for the lack of prior notification.
"I strongly believe we should have been consulted, the law should have been followed and I very much regret that wasn't the case," she said.
In Poland, Mr Obama said his administration had consulted Congress "for some time" about the possibility of a prisoner exchange, but Congress was not briefed ahead of the specific operation because they needed to seize the opportunity amid concerns about Sgt Bergdahl's health.
White House spokeswoman Caitlin Hayden also argued that delaying the soldier's transfer in order to comply with Congressional rules could have put the deal at risk.
Republican Senator John McCain called the Afghans released in the swap "wanted war criminals" who have "dedicated their lives to destroying us".
"This decision to bring Sgt Bergdahl home - and we applaud that he his home - is ill-founded, it is a mistake and it is putting the lives of American servicemen and women at risk. And that to me is unacceptable."
House Speaker John Boehner later backed calls for Congressional hearings into the matter, saying it was "important that we get clarity" about how the exchange came about.
According to Reuters news agency, Secretary of Defense Chuck Hagel has been invited by the House of Representatives Armed Services Committee to testify at a hearing on 11 June looking into the prisoner exchange.
The deal was defended by the top-ranking member of the military.
On his Facebook page, Gen Dempsey, chairman of the joint chiefs of staff, wrote the operation was the last opportunity to free the US captive.
When he is able to provide the facts, we'll learn what happened, he said, and he is innocent until proven guilty.
"Our Army's leaders will not look away from misconduct if it occurred. In the meantime, we will continue to care for him and his family."
Secretary of the Army John McHugh later said the Army would review the circumstances of his disappearance and captivity, but his health was currently the Army's first priority.
Sgt Bergdahl is in a stable condition in a military hospital in Germany.
Fellow soldiers have expressed frustration that others - reportedly six soldiers - were killed during the initial search for Sgt Bergdahl.
Fellow platoon member and former Sgt Matt Vierkant told US media he was more angry now than ever before.