The United States came under renewed pressure Tuesday to free the last Briton held at Guantánamo Bay, with U.K. parliamentarians demanding his repatriation amid fresh suggestions that U.S. officials looked into forcibly sending him to Saudi Arabia in a bid to silence him over torture claims.

In a debate in the House of Commons, allegations were aired that the sole reason Shaker Aamer — who has spent 13 years at the controversial U.S. prison in Cuba despite never being charged with a crime — has not been released was due to human rights abuses he witnessed in captivity, which U.S. and U.K. authorities would rather not come to light.

Despite being repeatedly pressed on the issue, to the extent of being called an apologist for the American regime, a foreign office minister attending the parliamentary session refused to divulge the explanations given by the U.S. authorities as to why Aamer remains behind bars.

Aamer, 46, a Saudi national and resident of the U.K., has been held at the U.S. detention facility without charge or trial since February 2002, despite being cleared for release twice, once by George W. Bush’s administration in 2007 and then by Barack Obama’s administration in 2009.

“Shaker’s release has become urgent,” said Labour Party MP John McDonnell during the parliamentary debate about his continued imprisonment. “We want Shaker released and returned to his family.”

During the debate, MPs raised what was described as deeply damaging allegations regarding the real reason some believe Aamer has not been released: that he was present during human rights abuses conducted by authorities.

U.K. Undersecretary of State for the Foreign Office Tobias Ellwood would not comment on the reasons given for Aamer’s continued imprisonment, saying to fellow MPs that “there are intelligence matters that I cannot discuss in this house.”

But he stated the U.K. government’s line that it wants Aamer back on U.K. soil, is looking for an "urgent resolution" to the case and will continue to raise the issue at the highest levels.

British Prime Minister David Cameron has discussed Aamer with Obama, who has pledged to make Aamer’s case a priority. Yet he remains in detention, his physical and mental health deteriorating, his lawyers say.

“It simply doesn’t add up. I do not see what the obstacles are,” Green Party MP Caroline Lucas said during Tuesday’s debate.

“It is a scandal that Shaker Aamer continues to languish in Guantánamo,” said Cori Crider, the director of Reprieve, the U.K.-based rights organization that represents Aamer.

He was picked up in Kabul, Afghanistan, in 2001 while doing work for an Islamic charity, his lawyers maintain. He is one of 122 detainees who remain at the detention facility at Guantánamo, 55 of whom have been cleared for release but are awaiting a country to take them.

Despite releasing 28 prisoners in 2014 — the most released since 2009 — Obama has failed to fulfill his promise to close the facility.

That has been due in part to congressional objections to releasing prisoners, but with Aamer cleared for release and the U.K. on record wanting him back, it is unclear why Aamer is still at Guantánamo.

Bernadette Meehan, White House National Security Council spokeswoman, said in January that Obama assured Cameron during a meeting that “we will prioritize this case while making sure any action taken is consistent with our national security."

Yet after the meeting between the U.S. and U.K. leaders, the U.S. secretary of defense at the time, Chuck Hagel, who had final say on Guantánamo releases, suggested to reporters that there were no outstanding files for him to sign regarding the Aamer case.

“I have made a decision on everything that is ready to be made a decision on,” he said during a press conference on Jan. 22.

In a statement to Al Jazeera on Tuesday, the State Department confirmed that the issue remains a priority.

“We are working to transfer each of the 55 detainees currently approved for transfer in a manner that protects our national security and is consistent with our humane treatment policies,” said Ian Moss, a senior adviser in the Office of the Special Envoy for Guantánamo Closure. “We recognize the importance the U.K. government has placed on resolving Mr. Aamer’s case in a timely manner, and we have made his case a priority.”

But there remain questions over whether the U.S. is more inclined to release Aamer to Saudi Arabia, despite concern that he may be at risk of abuse there.

According to documents obtained by human rights group Amnesty International after a Freedom of Information Act request, the U.S. and Saudi Arabia have had several communications about Aamer’s case during the Obama presidency.

One such action request was sent by the State Department to the embassy in Riyadh in 2010, weeks after then–Secretary of State Hillary Clinton wrote to then–British Foreign Minister William Hague about U.S. and U.K. officials meeting to discuss Aamer’s case.

“These records documenting U.S. government communications with the Saudi and British governments regarding Shaker paint a disturbing picture,” said Ramzi Kassem, a professor of law at the City University of New York who directs the Immigrant and Non-Citizen Rights Clinic, which represents prisoners at Guantánamo, including Aamer. “Yet the U.S. government seems to be exploring the option of forcibly sending him to Saudi Arabia anyway, despite the fact that the U.K. government has publicly called for his return.”

Kassem suggested the one possible reason some government officials might want Aamer sent to Saudi Arabia rather than the U.K. is that there he would be prevented from speaking about his detention.

While the documents make clear that the U.S. has held several discussions over Aamer’s status and possible release with U.K. and Saudi Arabia, redactions make it difficult to say exactly what those talks have entailed and why he remains at Guantánamo.

“We need a concrete timetable for his return home, and we must see answers on why this didn’t happen years ago,” Crider said. “For a start, we need to know what happened in secret meetings between the U.K. and U.S. and the U.S. and Saudi Arabia. Are these indications of an attempt to silence him by handing him over to the Saudi regime?”

Still, some human rights lawyers working on cases of detainees under U.S. control say it would not be the first time Washington has released detainees to countries where they were subject to abuse.

“The U.S. has a long record of sending Guantánamo detainees back to their home countries against their will, often for questionable reasons and with tragic results for those men,” said Wells Dixon, a senior staff attorney for the Center for Constitutional Rights.

With additional reporting by Jenifer Fenton and Matt Williams.