MINNEAPOLIS (AP) -- The deadly terror attack on a Nairobi mall has stirred concern about Westerners' involvement in the militant group that claimed responsibility. Kenyan President Uhuru Kenyatta said Tuesday that "initial reports had suggested that a British woman and two or three American citizens may have been involved in the attack," but that there hadn't been confirmation.
In Minnesota, where at least 22 young men have traveled to Somalia since 2007 to join al-Shabab, the FBI said this week its investigation of the terror group's recruiting is active and remains a priority.
Kyle Loven, a Minneapolis FBI spokesman, said he couldn't confirm any American involvement in the attack.
Here's a look at some of the issues and background fueling the concern:
Minnesota, mainly in the Minneapolis-St. Paul area, is home to the largest Somali community in the United States, including people who fled the long civil war in their east African country and children born in the United States. Many are now American citizens.
Al-Shabab's initial recruitment efforts began in 2007 when small groups began discussing returning home to fight Ethiopian troops who entered Somalia to prop up a weak U.N.-backed government and were seen by many Somalis as foreign invaders. The recruiters aimed their appeal at the young men's patriotic and religious ideals.
Even after Ethiopians were expelled from Somalia, al-Shabab continued to target young men frustrated with life in the West, luring them with propaganda videos that glorify jihad and martyrdom. A high-quality video that began circulating last month featured what it said were three Minneapolis men who were killed in Somalia.
According to Valentina Soria, a security analyst with London-based IHS Jane's, al-Shabab has increasingly focused in the past three years on the recruitment of western nationals and members of the Somali diaspora in the U.S. and Europe to offset its declining domestic support.
THE TRAVELERS' FATES
The FBI won't give current figures, but court filings and testimony from prosecutions show at least six men from Minnesota have died in Somalia since 2009.
They include Shirwa Mohamed Ahmed, who was 26 when he drove an explosives-laden truck into an office in 2009. The FBI has said he's believed to be the first U.S. citizen to carry out a suicide bombing. While it's unconfirmed how most of them met their ends, at least one other was a suicide bomber and at least two died in clashes with pro-government forces.
At least 18 men and three women have been charged in the Minnesota investigation. Some were travelers while others were accused of aiding the effort mainly by raising money. Seven men pleaded guilty to various charges while one man was convicted on terrorism-related charges last year. Two women were convicted in 2011 of being fundraisers for al-Shabab. A third woman pleaded guilty last month to lying to a grand jury. The other defendants remain at large or are dead or presumed dead.
WHY IT MATTERS IN THE WEST
Authorities have said in the past they are concerned that Americans who travel to Somalia might someday carry out attacks elsewhere, including in the U.S.
"Americans should be concerned about this because these are American citizens who are traveling to Africa ostensibly to engage in fighting and terrorist activities on behalf of foreign groups. ... Just as we wouldn't want foreign fighters in the United States, we should be doing everything in our power to prevent Americans from engaging in these kinds of activities overseas," Loven said.
The president of Somalia, Hassan Sheikh Mohamud, said in a speech Monday in Ohio the reports that some of the attackers may have been Somalis who lived in the United States illustrate that al-Shabab presents a threat not just to the region or Africa but to the world at large.
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