In this March 30, 2010, file photo, a U.S. service member stands in the turret of a Humvee at Guantanamo Bay, Cuba. (AP Photo/Brennan Linsley, File)

The Obama administration on Monday transferred 15 detainees from the U.S. military prison at Guantanamo Bay, Cuba, to the United Arab Emirates, the largest release under the current president, the Pentagon said.

The transfer comes as the president faces a looming deadline to keep the promise he made on his first day in office to close the military prison. The detainee population there dipped under 100 for the first time in years in January with the release of 10 Yemeni prisoners, and will shrink to 61 with the latest transfer, underscoring a late effort to move toward closure.

“The United States is grateful to the Government of the United Arab Emirates for its humanitarian gesture and willingness to support ongoing U.S. efforts to close the Guantanamo Bay detention facility,” the Pentagon said in a statement. “The United States coordinated with the Government of the United Arab Emirates to ensure these transfers took place consistent with appropriate security and humane treatment measures.”

The move was immediately condemned by Edward R. Royce (R.-Calif.), the chairman of the House Foreign Affairs Committee. He accused the Obama administration in a statement of “doubling down on policies that put American lives at risk” and “recklessness.”

“Once again, hardened terrorists are being released to foreign countries where they will be a threat,” Royce said. “Too many have already died at the hands of former detainees.”

Human Rights First praised the new transfer, which was first reported by Agence France-Presse, releasing a statement from retired Marine Maj. Gen. Michael Lehnert. He oversaw the construction of the prison in 2002 and said that it will “significantly hinder” national security until it is closed.

“We can only win the fight against terrorism and religious extremism if we adhere to American values,” Lehnert said. “Guantanamo flies in the face of those ideals we hold dear, and will continue to impede our efforts to keep Americans safe so long as it remains in operation.”

The newly released detainees include Zahar Hamdoun, a Yemeni who had been held without charges at Guantanamo since 2002 and had been considered among the so-called “forever prisoners” who were slated for indefinite detention. He was associated by U.S. intelligence officials with al-Qaeda, but was cleared for release in December by a U.S. task force including officials from several agencies. The Center for Constitutional Rights, which represents Hamdoun, said that he felt happy and hopeful but has been made a refugee by a U.S. policy that bans sending detainees back to their own countries.

Another detainee released Monday goes by just one name, Obaidullah, and was detained by U.S. troops in a raid in Afghanistan in 2002. The U.S. government once alleged that he associated with members of both al-Qaeda and the Taliban, and that he was captured along with mines and notebooks that showed how to make improvised explosive devices. He denied that before a military tribunal. He said he received some training from the Taliban but was forced into it. He also alleges he was abused while in U.S. custody.

The transfers this year have involved a number of countries that agreed to resettle detainees, including Serbia, Italy, Montenegro, Saudi Arabia, Senegal, Oman and Kuwait. The UAE last accepted detainees with the transfer of five men approved in November.

President Obama made an appeal in February for Congress to allow him to close the prison, a plan many lawmakers oppose. The administration released a blueprint for doing so in February and said at the time that of the 91 detainees still being held, 35 were eligible for release. As of Monday, 20 detainees remain at Guantanamo who are cleared for release, including some approved since February, said Navy Cmdr. Gary Ross, a Pentagon spokesman.

A number of detainees, including the alleged organizers of the 9/11 attacks, are facing war-crimes charges in military commissions. The administration has also said that other detainees are too dangerous to release but that there is not enough evidence against them that can be used in court, so they will be held indefinitely without charge.

The Obama administration believes that at least 12 detainees once held at Guantanamo have launched attacks on U.S. or allied troops in Afghanistan, killing about six people, U.S. officials acknowledged this year. All of the detainees involved were released under the administration of George W. Bush, U.S. officials said.