Washington (CNN) -- U.S. counterterrorism officials are investigating possible links between the attempted Northwest Airlines bombing and two former Guantanamo Bay prisoners who say they are leaders in an al Qaeda-affiliated terrorist group based in Yemen, U.S. officials told CNN on Tuesday.
The organization, al Qaeda in the Arabian Peninsula, has claimed responsibility for the attempted bombing, and the alleged bomber, Umar Farouk AbdulMutallab, was in Yemen this month.
The two self-proclaimed leaders of al Qaeda in the Arabian Peninsula were released from the U.S. detention facility in Guantanamo Bay, Cuba, in 2007 and sent to Saudi Arabia, according to a Department of Defense report on former detainees at Guantanamo who have returned to terrorism activities.
The unclassified version of the Defense Intelligence Agency report was released publicly last April and highlights former detainees who have carried out or are suspected of having carried out terrorist attacks after being released from the prison.
According to the report, Abu Sufyan al-Shihri was released from Guantanamo in November 2007 and sent to Saudi Arabia; Mazin Salih Musaid al-Alawi al-Awfi was released in July 2007 and sent to Saudi Arabia.
The report says the two men released a video last January announcing their leadership in the new organization, al Qaeda in the Arabian Peninsula.
That announcement led to questions about how many other former Guantanamo detainees may be planning to carry out terrorist attacks.
Pentagon officials have not released updated statistics on recidivism, but the unclassified report from April says 74 individuals, or 14 percent of former detainees, have turned to or are suspected of having turned to terrorism activity since their release.
The data represent the most recent publicly available statistics on former detainees tracked by military and other U.S. government intelligence agencies.
Of the more than 530 detainees released from the 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 the report's release, the total number of released detainees has risen to about 560, Pentagon officials said.
Pentagon statistics indicate that there was a slight increase in the release of detainees from Guantanamo at the end of 2008, and the number of released detainees turning to or suspected of turning to the insurgency is almost double, from 7 percent a few years ago, Pentagon officials familiar with the information told CNN.
The report said that between December 2008 and March 2009, nine former detainees were added to the confirmed list; six of them had been on the suspected list.
The Pentagon categorizes as "suspected" any former Guantanamo detainee about whom significant reporting indicates involvement in terrorist activities.
The report categorizes as "confirmed" any former detainee identified as involved in terrorist activity by a preponderance of evidence -- such as fingerprints, DNA, photo match or reliable or well-corroborated intelligence.
"What's clear is we are not seeing recidivism on the decline," said a defense official who declined to be identified because of the sensitivity of the issue.
Pentagon spokesman Bryan Whitman declined to say what officials think is the reason for the increase, but said the United States monitors released detainees as well as it can.
The Pentagon's report on recidivism identified almost 30 former detainees confirmed or suspected to have gone on to fight, including al-Shihri and al-Awfi, and includes examples of what these men did after their release.
The report also cited others:
• Abdullah Saleh Ali al-Ajmi, who was released in 2005 to Kuwait. In April 2008, he blew himself up in Mosul, Iraq, killing a number of Iraqis.
• Mohammed Ismail was released from the U.S. detention facility at Guantanamo Bay in early 2004 and returned to Afghanistan to be set free. Within four months, the U.S. military said, he was recaptured in Afghanistan attacking U.S. troops there, with paperwork that said he was a Taliban member in good standing.
• Abdullah Gulam Rasoul, who was released from Guantanamo in December 2007 and set free in Afghanistan, has become a powerful Taliban military commander in southern Afghanistan, and the United States suspects he is responsible for several attacks on U.S. forces there, the military said.
A senior U.S. military official last May said he believes Rasoul is using his Guantanamo experience to build on his "rock star status" among the Taliban.
The U.S. military had no updated information on the status of Rasoul for this story.
The Pentagon report also cited men sent home to Morocco who were later captured and accused of recruiting people for al Qaeda in Iraq; two men freed in Saudi Arabia who became leaders in a new al Qaeda organization there; and a Russian sent home who later was arrested for playing a role in a gas line bombing.