More than 40 Americans have been recruited by al-Shabab and gone to Somalia to join the fight, and at least 15 of them have been killed, Rep. Peter King, R-N.Y. said. The figures are based on his committee's investigation into the threat.
The findings come during the third in a series of hearings on the threat of Islamic radicalization in the U.S. Some feel the Republicans are unfairly singling out Muslims. They say focusing too closely on Islam and the religious motives of those who have attempted terror attacks threatens to alienate an entire community.
The majority of the recent terror plots against the U.S. have involved people espousing a radical and violent view of Islam.
The U.S. government has said at least 21 Americans are believed to have traveled to Somalia to join the terror group, which began as a push to expel Ethiopian soldiers, and at least four young men have been confirmed dead. Al-Shabab has expanded its focus over the years, and it has aligned itself with other anti-Western terror groups.
The top Democrat on the committee, however, said the threat posed by al-Shabab to the U.S. has been overstated.
"Al-Shabab does not appear to present any danger to this homeland," Thompson said.
Testifying at the hearing, former assistant U.S. attorney in Minnesota W. Anders Folk said a significant threat is posed by men and women who leave the U.S. to be trained by terror organizations and adopt an interpretation of Islam that justifies violence, and who then return to the U.S.
Associated Press reporter Amy Forliti in Minneapolis contributed to this story.