Six Yemeni detainees held at Guantanamo Bay for 13 years were transferred late Friday night to Oman, a country on the Arabian Peninsula that borders Yemen, the Pentagon said.

The resettlement of the Yemenis, who have all been cleared for release for years and have never been charged with a crime, is the first transfer approved by Secretary of Defense Ash Carter, who has been on the job for just four months. Four of the five detainees released from Guantanamo last January — all Yemenis — were also transferred to Oman. The US won't send any of the Yemeni Guantanamo detainees home due to instability and turmoil in Yemen.

"The United States is grateful to the Government of Oman for its humanitarian gesture and willingness to support ongoing US efforts to close the Guantanamo Bay detention facility," the Pentagon said in a statement. President Barack Obama met with Oman's deputy prime minister last month at the Gulf Cooperation Council summit at Camp David. "The United States coordinated with the Government of Oman to ensure these transfers took place consistent with appropriate security and humane treatment measures."

The Guantanamo detainee population now stands at 116 men, with 51 cleared for release. Obama has now released more than half of the 242 detainees who were being held at the detention facility when he took office in 2009.

The Pentagon said in a news release that Congress was notified about the transfers 30 days in advance as required by law. An administration official told VICE News that Carter has not notified Congress of any additional detainee transfers.

The detainees were transferred just as Congress is trying to pass a defense appropriations bill, known as the National Defense Authorization Act (NDAA), which contains provisions that would make it tougher for Obama to fulfill his campaign pledge of shuttering the detention facility by dictating how funds governing the transfer of detainees are used.

The White House on Tuesday opposed a version of the bill in the House, saying three sections related to Guantanamo would "restrict the Executive Branch's ability to manage the detainee population at the Guantanamo Bay, Cuba detention facility."

"Operating the detention facility at Guantanamo weakens our national security by draining resources, damaging our relationships with key allies and partners, and emboldening violent extremists," the White House's Office of Management and Budget said of the House bill. "These provisions are unwarranted and threaten to interfere with the Executive Branch's ability to determine the appropriate disposition of detainees and its flexibility to determine when and where to prosecute Guantanamo detainees based on the facts and circumstances of each case and our national security interests."

Carter and White House counterterrorism adviser Lisa Monaco are reportedly working on a plan to close Guantanamo.

Earlier this year, Senator John McCain, the chairman of the Senate Armed Services Committee, teamed up with Senators Kelly Ayotte, Lindsay Graham, and Richard Burr to introduce the Detaining Terrorists to Protect America Act of 2015. The legislation would have placed a two-year moratorium on the transfer of Guantanamo detainees who the military deemed to be medium and high risks at the time they were captured.

At the time, McCain said he supported closing Guantanamo but he was frustrated that the Obama administration didn't have a plan for closing the facility. A government task force has deemed several inmates too dangerous to transfer, and said that there is not enough evidence to prosecute others.

"For many years, I have believed that it would further US national security interests to close the Guantanamo detention facility. I still do," McCain said last February. "The problem is that, for more than six years now, the Obama Administration has offered no comprehensive plan to responsibly close the Guantanamo detention facility… What we now have instead is the perception of a president rushing to fulfill a political promise."

Now, according to news reports, McCain is working with Carter and Monaco and trying to secure support from the Republican-controlled Congress to support a Senate bill that would grant the administration the funding it needs to close Guantanamo and authorize the transfer of detainees to the US for continued detention or trial.

The captives who were transferred Friday were sent to Guantanamo exactly 13 years ago this month. They were at one time considered to be "high-risk," the criteria that Ayotte, Graham, Burr, and McCain had said should make them ineligible for transfer.

Myles Caggins, a Pentagon spokesman on detainee issues, said decisions to transfer detainees are made only after "detailed, specific conversations with the receiving country about the potential threat a detainee may pose after transfer and the measures the receiving country will take in order to sufficiently mitigate that threat, and to ensure humane treatment."

"The measures taken must be tailored to mitigate the specific threat that the detainee may pose," Caggins said. "If we do not receive adequate assurances, the transfer does not occur."

One of the six men released Friday night, Emad Abdullah Hassan, 35, was a longtime hunger striker. He was captured in Faisalabad, Pakistan in March 2002 during a raid jointly conducted by the CIA, FBI, and Pakistani intelligence. The raid also netted the CIA's first high-value detainee, Abu Zuabdyah, who is currently detained at a top-secret camp at Guantanamo. The five other detainees who were released Friday night were also captured in Pakistan.

'Operating the detention facility at Guantanamo weakens our national security by draining resources, damaging our relationships with key allies and partners, and emboldening violent extremists.'

Hassan had waged a high-profile federal lawsuit to end his force-feeding. According to his lawyers at the international legal organization Reprieve, Hassan had been on a hunger strike since 2007 and was "abusively force-fed more than 5,000 times since 2007 as part of the military's efforts to break his hunger strike."

Last year, Hassan wrote a letter to a federal judge appealing to her to "follow her faith" and put an end to the force-feeding at the detention facility. He ended his letter by asking one of his attorneys to send him Game of Thrones.

"Oman's decision to take men from Guantanamo is hugely welcome and we are relieved that Emad Hassan's terrible ordeal of being held for years despite being cleared for release is over," said Cori Crider, Hassan's attorney and the director of the international legal charity Reprieve.

The other detainees who were transferred are in their mid-30s and early 40s. The military does not provide birthdates for the men, only their year of birth. They include Idris Ahmad 'Abd Al Qadir Idris, suspected by the military of being one of the so-called "Dirty 30," a phrase used by US intelligence personnel for men accused of being bin Laden's bodyguards, or those who were attached to his security detail.

Transferred detainee Sharaf Ahmad Muhammad Mas'ud is an accused "Islamic extremist and an al Qaida-affiliated fighter" whose 2008 detainee assessment file released by Wikileaks said, "Has verbally expressed his distain for America and President Bush, and has encouraged and led mass disturbances among the other detainees." (The veracity of the intelligence in the military's detainee case summaries has been called into question by human rights groups.)

The others are Jalal Salam Awad Awad, also accused of being Bin Laden's bodyguard; Saa'd Nasser Moqbil Al Azani, accused of being "a senior al Qaida member and a close associate of Usama Bin Laden's religious advisor" whose name "appears on al Qaida-associated documents; and Muhammad Ali Salem Al Zarnuki, an alleged al Qaeda member who served on the front lines in Afghanistan as part of Bin Laden's "55th Arab Brigade."

Congressman Michael McCaul, the Republican chairman of the House Homeland Security Committee, criticized the transfer Saturday and said Obama is "giving potential terrorists the ability to return to the fight.

"Despite the high terror threat to our country, the President continues to open the jail cells at Guantanamo Bay ... The lack of a comprehensive detainee policy has led this President to make reckless decisions affecting American security," McCaul said in a statement. "The President needs to be up front with the American people, rather than have the release of dangerous detainees buried in a Saturday news dump."

The congressman also said the detainee transfers took place "despite the President's own intelligence advisors having confirmed that one-third of released detainees have re-engaged in terrorism."

But McCaul's math is flawed. He arrives at the 30 percent recidivism rate by combining the number of detainees confirmed of reengaging in terrorist activities with those suspected of reengagement. Caggins, the Pentagon spokesman, told VICE News that "more than 90 percent of the detainees transferred under [the Obama] administration are neither confirmed nor suspected by the intelligence community of reengagement."

One detainee who was not transferred Friday and had long been rumored to be released this month is Shaker Aamer, the last UK detainee. Aamer has been held at the detention facility for more than 13 years, and was cleared for transfer by both the Bush and Obama administrations. Aamer, 47, a Saudi national, is one of Guantanamo's highest profile captives. He has never been charged with a crime, and his ongoing detention has caught the attention of legendary singer Roger Waters of Pink Floyd. Aamer wrote a letter to Waters and quoted lyrics from the Pink Floyd album _The Wall. _Waters filmed a video in which he reads the letter and discusses Aamer's case. In addition to Waters, singer PJ Harvey wrote a song titled "Shaker Aamer," and other celebrities have rallied behind Aamer calling for his release.

Last week, four members of the British Parliament published an op-ed in the _New York Times_under the headline, "Obama's Slap in the Face to Britain," in which they expressed anger and frustration over the fact that there is no set timeline for Aamer's release, despite the fact that the White House told Britain's Prime Minister David Cameron last January that he would prioritize Aamer's case.

The members of Parliament traveled to Washington late last month to meet with administration officials and senators to discuss Aamer. They wrote that they were "astonished" to find that no one they met with in Washington seemed to know anything about Aamer's case.

The "lack of knowledge about Mr. Aamer's case indicates a troubling failure by the White House to communicate the importance of it," the members of Parliament wrote.

They said they heard that the holdup over transferring Aamer back to the UK might be due to "security considerations."

"Any suggestion that Britain does not have the legal structures, the security and intelligence skills, or the care capacity to address any issues with Mr. Aamer is deeply insulting," they wrote.

A senior administration official would not discuss with VICE News specific details of Aamer's case, or say when he may be released.

"I do not have a timeline on when particular detainees will be transferred from Guantanamo," the official said. "However, the Administration is committed to reducing the detainee population and to closing the detention facility responsibly."