Congressional Republicans are vowing to stay vigilant and prevent President Obama from closing the prison at Guantanamo Bay as the Senate begins to consider a defense authorization bill.

The new round of fights over the military prison comes with the administration in talks with Yemen and working with the United Nations to establish a rehabilitation center in the mideast country which could take in Gitmo detainees, as reported by the Washington Examiner.

Sen. Kelly Ayotte, R-N.H., said those efforts had rekindled concerns about the administration's desire to shutter Guantanamo Bay.

“I’m always concerned about the treatment of detainees,” said Ayotte, “and I’m more concerned lately.”

The Senate wants to approve the National Defense Authorization Act, which sets spending levels for the nation’s defense and security programs, before the Thanksgiving holiday. The Senate Armed Services Committee approved a $625 billion version of the bill back in June.

But with the measure headed for floor debate, it has become the vehicle for a number of thorny national security issues, including government spying programs, protections for victims of military sexual assault cases and the future of Gitmo.

The Guantanamo Bay issues are particularly vexing for the Obama administration, with the president vowing to close the facility despite staunch opposition from Congress.

Sen. Lindsey Graham, R-S.C., has been open to closing the facility, acknowledging that it is a rallying cry for critics of the U.S. abroad and a terrorist recruiting tool. But Graham, the chief architect of the military commissions bill, wants to make sure that if Gitmo is closed, safeguards are taken to prevent detainees from posing a future threat to the U.S.

The South Carolina lawmaker earlier this week conceded that there’s no ready solution to the issue.

“Frankly, we’re stuck,” he told reporters, noting that he and his Senate colleagues are working on a number of Gitmo-related amendments on the NDAA.

The administration is speaking with the Yemeni government about establishing a rehabilitation center outside the capital of Sana’a to help transition detainees from that country back to freedom.

More than half of the 164 prisoners who remain at Guantanamo Bay are from Yemen, so any effort to transfer them back to their home country would go a long way in helping Obama fulfill his promise to close the island prison.

The House version of the defense authorization bill keeps the prison open and bars the administration from transferring detainees unless they receive a special waiver from Secretary of Defense Chuck Hagel certifying that he does not believe they will pose a future terror threat.

Ayotte said she is deeply concerned about the potential recidivism rate for all prisoners released and intends to offer an amendment to the defense bill banning any transfers from Gitmo to Yemen.

“I don’t know how you can guarantee the security there — the government is tenuous in Yemen, there’s a whole host of issues — ungoverned territories,” she said. “I just think there are huge questions on whether you can guarantee the security of someone who is transferred from Gitmo to Yemen that they don’t get back into the fight.”

The Obama administration had lifted a ban on detainee transfers to Yemen earlier this year. But in August, the State Department was forced to shutter a record number of embassies across the Arab world in the face of a terrorist threat emanating from Yemen and Pakistan, raising concerns about repatriating detainees to those countries.

Senate Intelligence Committee Ranking Member Saxby Chambliss, R-Ga., has warned the Obama administration not “to experiment with sending Guantanamo detainees back to a terrorist hotbed like Yemen.”

Fears over former detainees returning to terrorism grew last week after the Washington Post, citing an internal Pentagon report, revealed that the Afghan government plans to release nearly 700 of 880 prisoners held at a high security facility in Kabul.

The U.S. turned over control of the prison earlier this year and had hoped that the Afghan government would continue to keep the detainees — many of whom were captured by U.S. special forces teams in dangerous raids — incarcerated. But Afghan leaders informed the Defense Department that most of those suspects would be freed. The report did not say what will happen with the 20 percent of prisoners Afghan officials deem too dangerous to release.

“Frankly, a lot of them belong in Gitmo — that’s one of the issues that need to be addressed in terms of Afghanistan,” said Ayotte. “I don’t know what the administration’s plan is.”

Ayotte and fellow Sen. Bob Casey, D-Pa., have voiced deep concerns about the prospect of Afghanistan turning into a safe-haven from which terrorists can operate and plan attacks on the United States and its allies.

Ayotte and Casey on Tuesday wrote a letter to Hagel and Secretary of State John Kerry, calling on the Obama administration to lay out a plan for the military's exit strategy from Afghanistan after the 2014 drawdown.

The senators fear that without a sufficient number of U.S. and international military trainers and other support personnel, the Afghan people risk losing the significant gains made in democracy, human rights and economic growth.

“We call on the administration to articulate a plan for our continued civilian mission and oversight of U.S. assistance programs that makes clear that America will stand with the Afghan people to prevent Afghanistan from reverting to the type of oppressive, intolerant and violent Taliban rule that served as fertile ground for al Qaeda,” they wrote.