WASHINGTON (AP) — The transfer of prisoners out of Guantanamo Bay has ground to a halt amid a slow Pentagon approval process.

That's caused frustration within the administration and raised doubts that President Barack Obama can fulfill his campaign promise to close the U.S. prison in Cuba for terrorism suspects.

A detainee sent back to Algeria in March is the only prisoner to have moved out this year, beyond the exchange of five Taliban members in return for U.S. Army Sgt. Bowe Bergdahl.

The slow pace is the result of a law giving Defense Secretary Chuck Hagel final authority to transfer detainees. Pentagon officials say they must consider the risks before signing off.

The White House says recidivism risks must be weighed against the danger of keeping the prison open.