A quarter of the detainees released from Guantanamo prison have likely joined global insurgencies or terror groups, the US director of national intelligence said in a report on Tuesday.
Of the 598 inmates released from the US facility in Guantanamo Bay, Cuba where suspected militants were rounded up after the September 11, 2001 attacks, 150 have either taken up arms or become involved in financing or recruitment, it said.
"Eighty-one (13.5 percent) are confirmed and 69 (11.5 percent) are suspected of reengaging in terrorist or insurgent activities after transfer," the intelligence oversight agency said.
Of those, the intelligence community believes 13 are dead, 54 are in custody and 83 remain at large, the report said.
It added, however, that of the 66 detainees released since January 2009, when President Barack Obama ordered a wide-ranging review of inmates, just two are confirmed and three are suspected of returning to combat.
But it added that "the number of former detainees identified as reengaged in terrorist or insurgent activity will increase."
Obama ordered Guantanamo prison shut down within a year in his January 2009 Executive Order, but he missed his deadline because of knotty legal issues and difficulties in finding third countries to take detainees.
The controversial detention center has long been a rallying point for anti-American sentiment and has been criticized by human rights groups.
But Obama's Republican opponents seized on the latest report as proof that the administration was acting too hastily in trying to close the facility.
"Unfortunately, these latest numbers make clear that fulfilling a campaign promise to close Guantanamo Bay is overriding what should be the administration's first priority - protecting Americans from terrorists," Kit Bond, the top Republican on the Senate intelligence committee, said.
"If one of these dangerous detainees attacks our troops or civilians, I don't know how the Administration will explain to the American people that we had him in custody, knew the risk he could return to the fight, and let him go anyway."
The prison, located on the Guantanamo naval base in Cuba, currently holds around 170 detainees, including three who have been convicted and 58 who have been placed in indefinite detention without trial.
Scores of other inmates have been transferred to third countries, where they have been released.
Efforts to try some Guantanamo detainees in civilian courts were dealt a major blow last month when a jury cleared a former inmate of all but one of the 286 charges brought against him for the 1998 US embassy bombings in Africa.