Thomas Watkins/Getty Images President Barack Obama is running out of time to fulfill his 2008 promise to close the Guantanamo Bay detention center.

WASHINGTON ― The Pentagon announced the transfer of 15 prisoners out of the Guantanamo Bay detention facility on Monday evening, marking the largest single exodus of detainees from the infamous prison in Barack Obama’s presidency.

The 15 men are being transferred to the United Arab Emirates, a country that accepted five Yemeni detainees last year because the U.S. ruled out repatriating them to their unstable home country. Because congressional restrictions currently outlaw transferring detainees to the U.S., the Obama administration has relied on other countries to take in prisoners who are cleared for release by an inter-agency review board.

There are now 61 prisoners at Guantanamo, including seven who are facing charges in the military commissions system, the war court at Guantanamo.

Large-scale detainee transfers were common under former President George W. Bush, but they slowed under Obama ― in part because of congressional limitations on releasing detainees. But 2016 has marked a renewed effort by the administration to shrink the prison population before Obama leaves office in January.

Even with help from allies, it’s unclear how Obama will be able to fulfill his campaign promise of closing Guantanamo without moving prisoners to another facility in the U.S. There is a group of detainees the White House refers to as an irreducible minimum ― meaning there is not enough evidence to charge them with a crime, but they are considered too dangerous to release.

Here are the 15 detainees who were released:

Abd al-Muhsin Abd al-Rab Salih al-Busi

Abd al-Rahman Sulayman

Mohammed Nasir Yahi Khussrof Kazaz

Abdul Muhammad Ahmad Nassar al-Muhajari

Muhammad Ahmad Said al-Adahi

Abdel Qadir al-Mudafari

Mahmud Abd Al Aziz al-Mujahid

Saeed Ahmed Mohammed Abdullah Sarem Jarabh

Mohammed Kamin

Zahar Omar Hamis bin Hamdoun

Hamid al-Razak (aka Haji Hamidullah)

Majid Mahmud Abdu Ahmed

Ayub Murshid Ali Salih

Obaidullah

Bashir Nasir Ali al-Marwalah

This article has been updated to include the names of those released.