WASHINGTON (Reuters) -- A classified Pentagon assessment shows one in five detainees released from the U.S. military prison at Guantanamo Bay has joined or is suspected of joining militant groups like Al-Qaeda, U.S. officials said.
The disclosure comes amid revelations that former detainees were playing a leadership role in Al-Qaeda in the Arabian Peninsula -- a Yemen-based group believed to be behind a failed plot to blow up a U.S. airliner on Christmas Day.
Under pressure to increase safeguards, President Barack Obama announced on January 5 that he had suspended the transfer of additional Guantanamo detainees to Yemen, citing the deteriorating security situation in the country.
A previous Pentagon assessment last April showed that 14 percent of former detainees had joined or were suspected of joining militant groups, up from 11 percent in December 2008.
Two officials, speaking on condition of anonymity, said the new Pentagon assessment showed the percentage had grown to 20 percent.
Pentagon press secretary Geoff Morrell declined to comment on the latest figures, saying they remained classified, but told reporters, "The trend hasn't reversed itself."
"This is an inexact science," Morrell said about whether enough screening was done of detainees in the past. "You know, we are making subjective calls based upon judgment, intelligence. And so there is no foolproof answer in this realm. That's what makes this so difficult."
But he added, "There needs to be a better accounting of detainees."
There are 198 prisoners left at the Guantanamo Bay detention facility, which once held 750, Pentagon officials said. Among those still being held there, roughly 91 are Yemeni.
Obama has encountered various complications in trying to close the Guantanamo facility and has acknowledged he will not be able to meet a self-imposed one-year deadline to close it that he promised when he took office last January.
Just last month, Obama's aides announced the U.S. government would proceed with buying an Illinois prison and is bolstering security there so a limited number of Guantanamo detainees can be transferred to it.
Morrell noted that Congress adjourned for recess without providing the military the authority or funding to transfer inmates to Illinois.
"Come the new year, when Congress reconvenes, I'm sure that the administration will be working aggressively with them to try to get both the funding and the authority to begin this process," Morrell said.