There are now 79 prisoners being held at the controversial facility in Cuba
US officials say a man who was being held at the controversial Guantanamo Bay prison has been transferred to Montenegro.
Abdel Malik Ahmed Abdel Wahab Al Rahabi's release is the first in a number expected from the military prison in Cuba.
A review found that the "continued law of war detention of Al Rahabi does not remain necessary to protect against a continuing significant threat to the security of the United States".
In a statement, the US defence department said: "The United States is grateful to the Government of Montenegro for its humanitarian gesture and willingness to support ongoing US efforts to close the Guantanamo Bay detention facility.
"The United States coordinated with the Government of Montenegro to ensure this transfer took place consistent with appropriate security and humane treatment measures," it added.
There are now 79 prisoners being held there, including 29 who have been cleared to be sent home or to other countries for resettlement.
Earlier this year, President Obama put forward his plan to close Guantanamo Bay.
However he now needs to get other politicians - including some fellow Democrats who have oppossed the closure - to back the plan in Congress.
Reports have suggested that President Obama has been considering whether to use his executive powers to override the Congressional ban on bringing detainees to the US.
Obama first entered an order to close Guantanamo Bay on his first day in office in 2008.