By David Bailey and Todd Melby

MINNEAPOLIS (Reuters) - Members of the largest ethnic Somali community in the United States expressed frustration on Tuesday, fearing a backlash after the attack on a Kenya shopping mall by a Somalia-based Islamic group that has recruited fighters in Minnesota.

It was unclear whether any of the attackers were connected to Minnesota's Somali community. But Somali-American leaders in Minneapolis were quick to condemn the assault after early unconfirmed reports identified one or more of the attacking al Shabaab rebels as recruits from the United States.

At least 20 young ethnic Somali men have left Minnesota since 2007 to join al Shabaab in Somalia, some dying there, U.S. authorities have said. The Minnesota Somali community has been the focus of a federal investigation since then.

An affiliate of al Qaeda, al Shabaab has been designated a terror organization by the United States. At least 67 people were killed in Nairobi's Westgate Mall, along with five of the attackers.

"This attack has generated a real concern among the Somali communities and fear of backlash," said Omar Jamal, a community activist and former head of the Somali Justice Advocacy Center.

"Every time things like this happen, the first thing that comes to the community's mind is whether there is a connection between here and there," Jamal said.

Zuhur Ahmed, 28, said she feared that men who go on the Islamic pilgrimage to Mecca will receive more security scrutiny. "The media attention is making it worse," she added.

Minnesota's ethnic Somali population has mushroomed in the last two decades from a small group to more than 50,000, due in part to generous social services for refugees, decent schools and a low cost of living, said Professor Abdi Samatar at the University of Minnesota, who arrived with his family in 1992.

"The people are nervous and worried about what the government might think," Samatar said. "I think most Minnesotans are easygoing people who know that you have to look at the individual separately from the collective, so to speak."

Story continues

The fact that Minnesota is seen as a focus of al Shabaab recruiting could be due to the size of the community, Samatar said.

The American Community Survey estimated the Minnesota population of Somali-Americans at more than 32,400 in 2010, or about one-third of its estimated 100,000 population in the United States.

Samatar said some refugees become alienated because they have left their home country and feel out of place, and more resources are needed to create opportunities for young men who might be vulnerable to a recruiter's message.

"Where we have put the focus, for some reasons legitimately, is only the monitoring and the security, which alienates the community even further," he said.

U.S. authorities have been investigating the recruitment of ethnic Somali men recruited into al Shabaab from the Twin Cities area of Minneapolis and St. Paul since 2007. The first group of recruits left the state for Somalia from October to December of that year, according to the FBI and court documents.

As of May 2013, U.S. authorities had charged 18 people with providing al Shabaab with material support in the form of cash, airline tickets or arranging faked itineraries for recruits headed to Somalia training camps. Eight were convicted.

The other 10 charged were fugitives or had been killed in Somalia, according to federal authorities. At least two men with Minnesota connections blew themselves up in attacks in Somalia.

U.S. connections for al Shabaab are not limited to Minnesota. Alabama-born Islamist Omar Hammami, commonly called Abu Mansoor al-Amriki, or "the American," was a leader in the al Qaeda-linked organization until he was killed earlier in September after a falling out with al-Shabaab's top commander.

Hammami was on Washington's most wanted list.

(Reporting by David Bailey and Todd Melby in Minneapolis and Richard Valdmanis in Boston; editing by Gunna Dickson)