Hennepin County Sheriff Rich Stanek told Congress on Wednesday he is concerned that Al-Shabab recruits who travel overseas to fight for the terrorist group could return home to launch attacks on American soil.

Testifying before the U.S. House Homeland Security Committee, Stanek told members that law enforcement faces an "uphill battle" to stop and monitor recruitment.

The panel hosted a hearing on the threat posed by Americans fighting in Somalia and Syria following last month's attack on an upscale shopping mall in Kenya.

"These individuals directly undermine our homeland security," said Republican U.S. Rep. Michael McCaul, the committee chairman. "They have been recruited inside the U.S., have left, and could potentially return – presenting a vast vulnerability in our counterterrorism efforts."

While defending Minnesota's Somali community, Stanek acknowledged that he shared McCaul's concerns, especially about recruits that may resurface in the Twin Cities.

Al-Shabab is Al-Qiada's affiliate in Somalia. Federal law enforcement officials estimate that at least 20 young men have left the state to join Al-Shabab's ranks since 2007.

"I do not have full confidence … that we have a full accounting of where they are, what they are doing or what they plan to do," Stanek told Republican U.S. Rep. Peter King of New York, an outspoken advocate for profiling of Muslims.

King and Minnesota U.S. Rep. Keith Ellison, a Muslim, have clashed over King's calls for law enforcement agencies to step up their surveillance of local Muslim communities as part of the War on Terror.

While obstacles remain for Al-Shabab recruits looking to re-enter the country, more must be done prevent attacks in America, said Stephanie Kostro, acting director of the Homeland Security Center for Strategic and International Studies.

"The United States and its allies and partners spend considerable resources – financial and human – in an effort to prevent and deter terrorist incidents," Kostro said. "But the nation cannot know the name and location of every individual who intends to do harm."