The United States transferred six Yemeni inmates from its Guantanamo Bay prison to Oman, the Pentagon said Saturday, part of a drive by President Barack Obama to close the controversial jail.

"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," a statement said.

The men arrived in the sultanate on Saturday for a "temporary stay," said an Omani foreign ministry statement carried by the official ONA news agency. It did not elaborate on their subsequent travel plans.

The six were named as Idris Ahmad Abd Al Qadir Idris, Sharaf Ahmad Muhammad Masud, Jalal Salam Awad Awad, Saad Nasser Moqbil Al Azani, Emad Abdallah Hassan and Muhammad Ali Salem Al Zarnuki.

Yemenis make up the largest portion of the prison population at Guantanamo. A total of 69 are still left at the jail, accounting for more than half of the 116 inmates remaining at the US naval base in southeastern Cuba.

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

The interagency Guantanamo Review Task Force "conducted comprehensive reviews of each of these cases," and a number of factors, including security issues, had been examined, it said.

"The decision to transfer a detainee is 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," said Lieutenant Colonel Myles Caggins, a Pentagon spokesman.

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

It was the second Guantanamo prisoner transfer this year, after the Pentagon announced in January that it had moved four men to Oman and one to Estonia.

A total 28 inmates were transferred out of Guantanamo in 2014.

- Struggling to empty Guantanamo -

Thwarted by Congress in his effort to close the prison, Obama has had to rely on a handful of countries that have agreed to accept detainees.

The prison was set up to hold alleged terror suspects after the September 11, 2001 attacks.

But human rights groups have condemned the jail as a "legal black hole" where inmates languish for years without being tried.

Caggins said the Pentagon took any attempt by the freed detainees to reengage with violent extremists "very seriously," insisting that few former Guantanamo inmates have attempted to do so.

"More than 90 percent of the detainees transferred under this administration are neither confirmed nor suspected by the intelligence community of reengagement," Caggins said.

But House Homeland Security Chairman Michael McCaul disagreed, saying a third of released detainees have engaged in terror, and calling the latest transfers "reckless."

"The lack of a comprehensive detainee policy has led this president to make reckless decisions affecting American security," McCaul said.

"The president needs to be upfront with the American people, rather than have the release of dangerous detainees buried in a Saturday news dump."

Of the 122 detainees transferred by the Obama administration, 75 have been resettled in third countries.

"We are working feverishly to transfer each of the 51 detainees currently approved for transfer," said Ian Moss, senior State Department advisor to the envoy on Guantanamo closure.

Of those, 43 are Yemeni nationals.

"It is not in our national security interest to continue to detain individuals if we as a government have determined that they can be transferred from Guantanamo responsibly," Moss said.