Washington (CNN) -- The number of former detainees once held by the U.S. in Cuba but now returning to terrorism activity has risen from 14 percent to 20 percent, according to a senior Defense official.
A classified report by the Pentagon's Defense Intelligence Agency (DIA) says that one in five former detainees returned or are suspected to have returned to terrorist activity after leaving the U.S. prison facility. That is an increase from 14 percent from a similar report by the DIA released in April, according to the official familiar with the new report.
Geoff Morrell, press secretary for Secretary of Defense Robert Gates, said last week that an unclassified version of the report is expected to be released, but the number of former detainees who have "returned to the fight" has gone up since last year and added, "I don't think that trend has reversed itself."
While the actual full detailed statistics on recidivism have not been released, the April 2009 report says 74 individuals have turned to, or are suspected of having turned to, terrorism activity since their release.
Of the more than 530 detainees released from the Guantanamo Bay prison between 2002 and last spring, 27 were confirmed to have engaged in terrorist activities, and 47 were suspected of participating in a terrorist act, according to Pentagon statistics cited in the spring report.
Since that report's release, the total number of released detainees has risen to about 560, Pentagon officials said.
Morrell did not offer a reason for the increase but said the department monitors former detainees the best it can.
"There is no foolproof answer in this realm, that's what makes this so difficult," he said.
Almost half of the remaining detainees at Guantanamo are from Yemen. President Obama halted the transfer of the remaining Yemenis back home after the failed Christmas Day bombing plot of a Northwest Airlines jet, an incident that allegedly had ties to Yemen.
The U.S. is investigating a former Guantanamo detainee, Abu Sufyan al-Shihri, released in 2007. He is a Saudi now based in Yemen and a self-proclaimed leader of al Qaeda in the Arabian Peninsula. The U.S. is trying determine if he was involved in planning the Christmas Day plot. Al Qaeda in the Arabian Peninsula has claimed responsibility for the attempted bombing.
Some 21 Yemenis have been released from the detention facility since 2002, 14 under the Bush administration and seven under the Obama administration.