Up to 30 former Guantanamo detainees released since 2011 have joined forces with the Islamic State, reports claim.

Of the 620 detainees released from the prison, around 200 are believed to be fighting with terrorist forces once more.

Senior defense forces believe 20 to 30 of those have joined Syrian groups such as ISIS, Fox News reports.

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ISIS connection? Defense sources claim up to 30 Guantanamo detainees have joined ISIS since their release

The suspects, whose identities have not been confirmed, are believed to have migrated to the Middle Eastern war zone from African and European countries which agreed to receive them from the United States.

And it is claimed they are now teaching fellow extremists torture methods allegedly used by the U.S. such as waterboarding.

The topic is the subject of heated debate as the Republicans release a new ad campaign suggesting President Obama's plans to move Guantanamo to the US will open the gates to ISIS-affiliated terrorists.

It says: 'ISIS gaining ground. Terrorists committing mass murder. Ebola inside the U.S. Americans alarmed about national security. What's President Obama doing? Making plans to bring terrorists from Guantanamo to our country... November 4th, Obama's policies are on the ballot. Vote to keep terrorists off U.S. soil. Vote Republican.'

According to a press statement, this message will air this week in Alaska, Arkansas, Colorado, Iowa, North Carolina, New Hampshire, Louisiana, and Virginia.

Recruiting: The Islamic State is believed to have recruited hundreds of fighters from across the world

Obama has vowed since his 2008 presidential campaign to close the prison camp, which critics say violates U.S. principles by keeping detainees locked up without trial.

The White House has long objected to congressional restrictions that would prevent the camp from closing.

'Our position right now, our policy right now, is seeking support from Congress to lift the restrictions that we feel are misguided,' said Eric Schultz, a White House spokesman.

Many Republicans consider the prison, which still holds about 150 prisoners, essential in the fight against international terrorism because it allows prisoners to be held outside the United States.

Despite numerous 'Since the president came into office in 2009 the administration has been examining all possible ways we could get to closure of the facility, but we are not drafting options to override the law,' said Caitlin Hayden, a spokeswoman for the White House National Security Council.

'We are continuing to work on transfers [of prisoners] and calling on Congress to lift restrictions.'

'Our position right now, our policy right now, is seeking support from Congress to lift the restrictions that we feel are misguided,' said Eric Schultz, a White House spokesman.

Danger? It comes as the Republicans release an ad warning against Obama's plan to move detainees to the US

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John Boehner, the Republican speaker of the House of Representatives, said on Thursday an 'overwhelming majority' of the American people opposed allowing prisoners from Guantanamo to enter the United States.

'Even as Islamic jihadists are beheading Americans, the White House is so eager to bring these terrorists from Guantanamo Bay to the United States that it is examining ways to thwart Congress and unilaterally re-write the law,' he said in a statement.

'Not only is this scheme dangerous, it is yet another example of what will be this administration's legacy of lawlessness.'