U.S. law enforcement authorities believe as many as three dozen Americans who converted to Islam in prison have traveled to Yemen, possibly to train with al-Qaida, according to a Senate report.
The "radicalization" of the individuals has alarmed U.S. officials even though no evidence has immediately tied them to terrorist activities.
Several of the individuals have "dropped off the radar" for weeks at a time and continue to carry U.S. passports, according to a copy of the report obtained by The Associated Press.
The assessment was written by staff working for Senate Foreign Relations Committee Chairman John Kerry, D-Mass.
"Al-Qaida's recruitment tactics also have changed," Kerry wrote in an introduction to the report. "The group seeks to recruit American citizens to carry out terrorist attacks in the United States."
Al-Qaida forces in Yemen have emerged in recent months as a pressing threat to U.S. security, with ties to the recent airline bombing plot and Fort Hood shooting.
The White House and Pentagon have said there are no plans to send ground troops there, and Yemen has made clear it wouldn't want them. Remaining options to defeat the terrorist threat there would include covert strikes against al-Qaida targets and increased aid to help train and equip Yemen's own security forces.
Gen. David Petraeus, the head of U.S. Central Command, has said he would like to double military aid to Yemen, which is currently about $67 million.
Hearing set on Yemen
Kerry's report was expected to set the stage for a Wednesday public hearing on Yemen with testimony from senior State Department officials.
In addition to its finding that al-Qaida was actively trying to attract "nontraditional followers" that could penetrate U.S. security, the staff report concludes that al-Qaida has remained a viable threat.
"Despite setbacks, al-Qaida is not on the run," the report concludes.
In addition to the nearly three dozen prisoners, Kerry's staff also cites as many as 10 non-Yemeni Americans who moved to Yemen, converted to Islamic fundamentalism and married Yemeni women to remain in the country.
"Described by one American official as 'blond-haired, blue eyed-types,' these individuals fit a profile of Americans whom al-Qaida has sought to recruit over the past several years," the report states.