Before the transfer of six inmates from the Guantanamo Bay to Oman, the prison held 122 detainees, with 57 approved for a transfer home or to a third country. Most of the prisoners at the top-security facility have never been charged with a crime. (Bill O'Leary/Post)

The Obama administration has moved six Yemeni detainees from the Guantanamo Bay detention center to Oman, the Pentagon said late Friday, the first time Defense Secretary Ashton B. Carter has approved a transfer from the military prison in Cuba since taking charge at the Pentagon in February.

Officials have said that Carter has been taking stock of the situation at Guantanamo, which President Obama has vowed to close before he leaves office in 2017. To allow Obama to make good on his promise, the Pentagon must resettle prisoners whom officials have deemed nonthreatening enough to go to a third country. This spring, officials had previewed plans to resettle as many as 10 detainees as early as June.

Before the latest resettlement, the prison held 122 detainees, with 57 approved for a transfer home or to a third country. Most of the prisoners have never been charged with a crime.

The Yemenis sent to Oman are Idris Ahmad Abdu Qadir Idris; Sharaf Ahmad Muhammad Masud; Jalal Salam Awad Awad; Saad Bin Nasser Ibn Mukbil al-Azani; Emad Abdallah Hassan; and Muhammad Ali Salam al-Zarnuqi. Allhave been in custody for more than 13 years.

“The United States coordinated with the government of Oman to ensure these transfers took place consistent with appropriate security and humane treatment measures,” the Pentagon said.

According to U.S. military files disclosed by the anti-secrecy group WikiLeaks, several were bodyguards for al-Qaeda leader Osama bin Laden before the Sept. 11, 2001, attacks. Many were described as seasoned fighters who traveled to Afghanistan and Pakistan for militant activities.

But senior U.S. officials have cautioned that under the Obama administration, those files were scrubbed and reevaluated. Some of the files’ information was discredited, the officials have said.

“The United States is very grateful to our partner, Oman, for this significant humanitarian gesture, and appreciates the generous assistance of the Government of Oman as we continue our efforts to responsibly reduce the detainee population and ultimately close the detention facility at Guantanamo,” Charles Trumbull, the acting special envoy for Guantanamo closure at the State Department, said in a statement Friday night.

The decision to approve transfers is a significant one for Carter, a veteran Pentagon bureaucrat. The hesitancy of his predecessor, Chuck Hagel, to approve transfers created friction with the White House before Hagel announced his resignation last year.

The pressure on Carter to quickly reduce Guantanamo’s population may be even greater, as lawmakers consider measures that would all but halt the administration’s plans to resettle inmates. While Sen. John McCain (R-Ariz.) has suggested that a compromise may be possible, other lawmakers have argued that moving or resettling detainees threatens U.S. security.

In the event Congress does not permit Obama to resettle more prisoners, White House officials have been exploring options for unilateral closure.

Officials said State Department officials originally negotiated a deal to transfer 10 Yemenis to Oman. But after a decision was made to split the transfers, four of the men were sent to Oman in January, the last transfer before this week. A fifth Yemeni was sent to Estonia in January.

A former U.S. official, speaking on the condition of anonymity to discuss detainee deliberations, said the Obama administration should be making progress “every month” in resettling prisoners who have been approved for transfer.

“Any month that goes by without a transfer is undermining the president’s policy and is unfair to the individuals involved,” he said.