WASHINGTON -LRB- CNN -RRB- -- There is an increasing threat of homegrown terror stemming from segments of a deeply isolated and alienated Somali-American community , a U.S. Senate committee hearing concluded Wednesday . Sen. Joseph Lieberman says a number of Somali-Americans support terrorist groups . The hearing , conducted by the Senate Homeland and Governmental Affairs Committee , focused on the attempted recruitment of young Somali-American men by al-Shabaab , `` a violent and brutal extremist -LRB- Somali -RRB- group '' with significant ties to al Qaeda , according to the U.S. State Department . `` Over the last two years , individuals from the Somali community in the United States , including American citizens , have left for Somalia to support and in some cases fight on behalf of al-Shabaab , '' noted the committee 's chairman , Sen. Joseph Lieberman , I-Connecticut . Al-Shabaab -- also known as the Mujahedeen Youth Movement -- was officially designated as a terrorist organization by the U.S. government in March 2008 . The hearing highlighted the case of Shirwa Ahmed , a 27-year-old Somali-American who had been radicalized by al-Shabaab in his adopted home state of Minnesota before traveling to Somalia and blowing up himself and 29 others in October . The idea that Ahmed was radicalized in the United States raised red flags throughout the U.S. intelligence community . The incident -- the first suicide bombing by a naturalized U.S. citizen -- was the `` most significant case of homegrown American terrorism recruiting based on violent Islamist ideology , '' Lieberman said . `` The dangers brought to light by these revelations is clear : radicalized individuals trained in terrorist tactics and in possession of American passports can clearly pose a threat to the security of our country , '' said Sen. Susan Collins , R-Maine . Segments of the Somali-American community have been made vulnerable to recruitment by al-Shabaab because of a particularly tumultuous adjustment to American life , noted Andrew Liepman , deputy director for intelligence at the National Counterterrorism Center . `` Despite significant efforts to facilitate their settlement into American communities , many Somali immigrants face isolation , '' Liepman said . `` The -LRB- tough -RRB- adjustment to American society has reinforced their greater insularity compared to other more integrated recent immigrant communities and has aggravated the challenges of assimilation for their children , '' he said . Somalis began arriving in the United States in significant numbers following the U.S. intervention in Somalia 's humanitarian crisis in 1992 , Liepman said . The Somali-American population is now concentrated in clusters primarily in Minneapolis , Minnesota ; Columbus , Ohio ; Seattle , Washington ; and San Diego , California . The potential recruitment of young Somali-American men has been made possible by `` a number of factors that come together when a dynamic , influential and extremist leader gains access to a despondent and disenfranchised group of young men , '' Liepman said . Many refugees , he said , `` lack structure and definition in their lives '' and are `` torn between their parents ' traditional tribal and clan identities and the new cultures and traditions offered by American society . '' Liepman pointed out that there was no evidence of a radicalization of the entire Somali-American community , now believed to number between 70,000 and 200,000 people . In fact , he said , the Somali-American community has been victimized by a `` small group of extremists who are essentially terrorizing their own community , who are recruiting and radicalizing young people within that community . '' `` We do n't have radicalized communities . We have radicalized clusters of -LRB- young -RRB- people , '' emphasized Philip Mudd , a director of the FBI 's national security branch . The potential terrorist indoctrination and recruitment was a consequence of these clusters , Liepman said , and is the product of `` the refugee experience of fleeing a war-torn country combined with isolation , perceived discrimination , marginalization and frustrated expectations . `` Local criminal familial and clan dynamics make some members of this community more susceptible to -LRB- this -RRB- sort of extremist influence '' of groups such as al-Shabaab , he said . Liepman said there is a serious concern about individuals being indoctrinated by al Qaeda and al-Shabaab while in Somalia and then returning to the United States `` with the intention to conduct attacks . ''