The US says it has sent 15 Guantanamo Bay detainees to the United Arab Emirates - the largest single transfer during President Barack Obama's administration.
The Pentagon says the transfer of 12 Yemeni nationals and three Afghans brings the total number of prisoners down to 61 at the US facility in Cuba.The released inmates had been held without charge, some for over 14 years.
President Obama wants to close the prison before he leaves office.
Obama want it closed because he believes Guantanamo Bay is contrary to US values, undermining the nation's standing in the world - a standing based on support for the rule of law.
Most inmates there have not been charged and, in February, Mr Obama lamented that "not a single verdict has been reached" on those there that have.
He also believes the facility fuels the recruitment of jihadists.
It's also expensive to run - $445m (£345m) annually.
However most republicans in the congress prefer it to remain open.