Pentagon delivers recommendations on Guantanamo Bay's future

"The Secretary of Defense has provided the White House with an updated policy governing the criteria for transfer of individuals to the detention facility at US Naval Station Guantanamo Bay," Pentagon spokesperson Cdr. Sarah Higgins told CNN.

"This policy provides our warfighters guidance on nominating detainees for transfer to Guantanamo detention should that person present a continuing, significant threat to the security of the United States," she added.

The Pentagon has not made the details of the recommendations public at this stage.

Trump's executive order, signed just prior to his first State of the Union, said Secretary of Defense James Mattis should "recommend policies to the President" on this issue "within 90 days." The recommendations were delivered one day after the deadline, according to a defense official.

Asked about the deadline, Mattis told reporters Monday that "right now I'm not working that issue."

In his State of the Union announcement Trump suggested he wanted to send more detainees to Guantanamo.

"I am asking Congress to ensure that in the fight against ISIS and al Qaeda we continue to have all necessary power to detain terrorists wherever we chase them down, wherever we find them. And In many cases for them it will now be Guantánamo bay," Trump said in January.

The US-backed Syrian Democratic Forces have captured over 400 foreign fighters during their campaign against ISIS, according to US defense officials. One of those detainees included a militant with links to the 9/11 terrorist attacks.

"We have been engaging with their home countries. Home being the country they were a citizen of when they left to go fight. Now, in some cases, those countries have stripped them of their citizenship, so they have a different view as far as what their status is today. So this is not simple," Mattis said of the foreign fighter detainees.

"Now that's being worked principally, of course, by State Department, and we're giving all the support that we can," he added.

The detention of an American citizen captured by US-backed forces fighting ISIS in Syria has been the subject on a month's long legal battle between the Department of Justice and the American Civil Liberties Union.