Most of the American men training with Al Shabaab are believed to have been radicalized in the U.S., especially in Minneapolis, according to U.S. officials. The FBI alleges that these young men have been recruited by Al Shabaab both on the Internet and in person. 

One such recruit from Minneapolis, 27-year-old Farah Mohamad Beledi, was one of two suicide bombers who attacked a military base in Mogadishu on May 30, 2011, according to the FBI. Two African Union peacekeepers and a Somali soldier were killed in the attack.

Beledi is the second confirmed American suicide bomber. The first, Shirwa Ahmed, carried out a suicide bombing at the Ethiopian Consulate and the presidential palace in Hargeisa killing 24 people in October 2009.  Federal investigators have also looked into reports about whether another American was involved in a suicide attack in Mogadishu in September 2009 that killed 21 people. The identity of that attacker has never been confirmed.

FBI director Robert Mueller said he was "absolutely" concerned that the young American men may return to the U.S. with their passports and attempt to carry out an attack on U.S. soil similar to the foiled plot in Australia, in which Somali-Australians allegedly affiliated with Al Shabaab planned to carry out a suicide attack on a Sydney army base after returning from Somalia.

While there have been no similar plots in the United States to date, Al Shabaab's desire to expand its operations outside of Somali and its ability to attract American recruits, presents a significant threat to the U.S.