US Defence Department officials broke the law by failing to alert Congress before releasing five Taliban members held at Guantanamo Bay military prison in exchange for a captured soldier, a government watchdog said.
The Government Accountability Office (GAO) said the Pentagon broke the law by using money appropriated by Congress to carry out the transfer of Guantanamo prisoners without giving the required 30-day notice.
The GAO assessment was requested by Republicans who were angered over the lack of notice they received about the decision in May to transfer five Taliban prisoners to Qatar in exchange for the release of army sergeant Bowe Bergdahl.
Senator Saxby Chambliss, vice-chairman of the Senate Select Committee on Intelligence, said the finding validated the view that President Barack Obama had "disregarded laws duly passed by Congress" by allowing a prisoner transfer that cost almost US$1 million.
The Pentagon insists the swap to recover Bergdahl was conducted lawfully.