Story highlights Sen. John McCain says Guantanamo could still be closed

But demands Obama administration offer clear plan

Congress banned detainee transfers to U.S. mainland in 2010

An unlikely ally is offering a glimmer of hope that President Barack Obama can make good on his vow to close Guantanamo Bay before leaving office.

Republican Sen. John McCain, a fierce critic of Obama's foreign policy, is about to take the chairmanship of the powerful Senate Armed Services Committee. He says it's still possible the war on terror camp in Cuba could be shut down -- but warns that the administration will have to come up with a clear plan to overcome Republican opposition.

Asked in a CNN interview whether he was prepared to help his old political foe, despite a congressional ban on sending detainees to the U.S. mainland, McCain said, "I am prepared to and I think it can be done."

But he warned that ever since he started talking to the administration about Guantanamo Bay in 2009, it had "never come forward with a plan as to how we treat those individuals that have been judged as too dangerous to ever be released, and that is the hangup."

McCain, himself a former prisoner of war, has long favored closing Guantanamo Bay, which critics say stains the reputation of the United States and is a recruiting tool for terrorists. But key players in Congress, including many senior Republicans, have barred funding for the administration to send remaining inmates elsewhere or to build facilities on the U.S. mainland.

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Speculation about the camp's future is being stoked by the recent transfers of a group of prisoners to Uruguay last week. The U.S. response to the 9/11 attacks in 2001 is also back in the spotlight because of the recent release of a Senate report on enhanced interrogation tactics critics say equate to torture.

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McCain said he thought that Republican opposition could be overcome, if the administration laid out exactly how it believed it could close Guantanamo.

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"If I went to the members of the committee today and said, 'Look they are going to be moved to a maximum security prison in some location in the United States of America and we have a plan for that transfer, I think most of them would be perfectly happy about that," McCain said.

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Last weekend, the Obama administration sent six Guantanamo Bay detainees to Uruguay for resettlement as refugees as part of its plan to depopulate the camp prior to its closure.

Four of the former detainees -- Ahmed Adnan Ahjam, Ali Hussain Shaabaan, Omar Mahmoud Faraj, and Jihad Diyab -- are Syrian nationals, while Abdul Bin Mohammed Abis Ourgy is Tunisian, and Mohammed Tahanmatan is Palestinian, according to Pentagon press secretary Rear Adm. John Kirby.

I just don't think that is trustworthy," McCain said, adding that former inmates needed re-education to ensure they did not return to extremism.

"I am very concerned," he said.

Republicans complain that released detainees are not sufficiently monitored when they leave Guantanamo Bay, and cite figures saying that nearly 30 percent of those released are back in the fight against U.S. forces.

The transfers leave only 136 detainees at Guantanamo Bay, out of an peak population of more than 750. That's the lowest number of inmates at the base in Cuba since detainees started arriving in 2002.

But that leaves the most problematic prisoners, including those who the administration says are too dangerous to be released, and cannot be tried in civilian courts as they are considered enemy combatants or the evidence against them is seen as tainted because it was obtained under duress.

The Wall Street Journal reported in October that Obama remained determined to close Guantanamo Bay, and was prepared to use executive power to do so if Congress would not go along.

Since he won re-election in 2012, Obama has appointed special envoys at the Defense and State departments to try to get foreign countries to accept more foreign detainees. He has also lifted the moratorium on lifting sending Yemeni prisoners back home.

Nearly all Guantanamo prisoners are being held without charges, and while about half of those are considered high-level threat detainees, the remainder were determined to be low-level threats by a task force of top U.S. intelligence and law enforcement agencies. Those in the latter group could gain their freedom, provided security conditions could first be met in their host countries.

In December 2010, Congress amended the annual defense budget bill to prevent the transfer of any Guantanamo detainees to the United States. That defeated the Obama administration's plans announced a year earlier to try several Guantanamo detainees involved in the 9/11 terrorist attacks in U.S. federal court.