Top Congressional Republicans have raised sharp questions about President Barack Obama's deal to swap five Taliban members for a captured US solder, with some even accusing him of breaking the law.
Several opposition Republicans issued statements welcoming Saturday's release of Sergeant Bowe Bergdahl.
But several Republicans also claimed that his exchange for "terrorists" held in the Guantanamo Bay detention centre would just encourage more kidnappings of US soldiers.
Lawmakers were not told of the Guantanamo prisoner transfer until after the swap, the Washington Post reported.
Mike Rogers, chairman of the House intelligence committee, said that he is "pleased that Sergeant Bergdahl is free and will be returning to his family in the United States."
However he was "extremely troubled" that US officials "negotiated with terrorists" to reach the swap deal.
"This fundamental shift in US policy signals to terrorists around the world a greater incentive to take US hostages," Rogers said.
"I believe this decision will threaten the lives of American soldiers for years to come," he said.
Influential Republican Senator John McCain demanded to know what steps were being taken to "ensure that these vicious and violent Taliban extremists never return to fight against the United States and our partners."
He described the men being released as "hardened terrorists who have the blood of Americans and countless Afghans on their hands."
The top Republicans on the House and Senate armed services committees were even harsher on Obama, claiming the president broke the law.
"America has maintained a prohibition on negotiating with terrorists for good reason," Representative Howard "Buck" McKeon and Senator James Inhofe said in a joint statement.
"In executing this transfer, the president also clearly violated laws which require him to notify Congress thirty days before any transfer of terrorists from Guantanamo Bay and to explain how the threat posed by such terrorists has been substantially mitigated."
The law was indeed not followed, a senior US official told the Post, speaking on condition of anonymity.
Obama believes that the law is unconstitutional because it limits his power as the US commander in chief, and therefore he can override it, the official told the Post.
Senate Majority Leader Harry Reid, a Democrat, congratulated Obama for "taking decisive action" to reach the deal.
The president "recognized our solemn obligation to take every possible measure to protect and defend the men and women who serve our nation," Reid said in a statement.
The transfer of the five Taliban members leaves 149 detainees in the US military prison in Cuba, including 12 Afghan nationals, four of whom have been approved for transfer.