A new report released by Republicans on the House Homeland Security Committee shows there's still a threat of Americans being recruited by Somali terror group and Al Qaeda ally Al Shabaab for the purpose of carrying out attacks in the U.S.

Committee chairman Rep. Peter King, R-N.Y. held a hearing Wednesday on Al Shabaab recruiting in America.  It was the third in a series of controversial "Muslim radicalization" hearings King has called.

"The key finding is that there is a looming danger of American Shabaab fighters returning to the U.S. to strike or helping Al Qaeda and its affiliates attack the homeland," the report reads. "U.S. intelligence underestimated the Pakistani Taliban and Al Qaeda in Yemen's capability of launching attacks here; we cannot afford to make the same mistake with Shabaab."

The report says at least 40 Americans have joined the terror group and 15 have been killed fighting for them. It also says 21 American Shabaab members are unaccounted for and that they pose a threat to U.S. security.

Many Democrats have bemoaned King's series of radicalization hearings, and while the ranking member of the committee Rep. Bennie Thompson, D-Miss., says Shabaab is an issue, he downplays its importance and says other types of terror should be focused on as well.

"The threat of Al Shabaab radicalizing young Americans is a problem we can constructively address," Thompson said in a statement before the hearing. "Today marks the third time that this committee has taken up alleged links between terrorism and the American Muslim community. Before these hearings began, I requested that their focus be broadened to include a look at the real and present threat of domestic violent extremism. Those requests were rebuffed."

Al Shabaab recruitment first came to the attention of Congress more than two years ago when the Senate Homeland Security Committee held hearings on the large number of Somali-Americans being recruited back to Africa for terror training.