MINNEAPOLIS — As American law enforcement agents pored over evidence collected from the deadly siege at a Nairobi shopping mall to learn, in part, whether those responsible had any ties to the United States, people of Somali descent here braced for what they fear could result in a new wave of stigmatization and scrutiny.

“Everyone is scared,” said Ahmed Hirsi, who helps lead a youth group in the Twin Cities, the heart of the nation’s largest Somali-American population. “The community is holding its breath — all over again.”

In an investigation that has unfolded since 2007, federal authorities concluded that more than 20 young men from Minnesota left for Somalia to join the Shabab, a Somali Islamist group that has been deemed a terrorist organization and linked to suicide bombings.

Now the Shabab have claimed responsibility for the attack that killed more than 60 people in the Westgate mall in Nairobi. A Kenyan official suggested on Monday that some of the attackers may have been from Minnesota, though American officials say they have not determined whether there is any link.

“If this sort of recruitment has somehow happened again, it takes us way back,” Mr. Hirsi said, adding that most in the community were vehemently opposed to the Shabab, revolted by the attack in Nairobi and appalled at the suggestion of a Minnesota connection.

“This is not who we are,” he said. “And if this turns out to be someone from here, everyone is going to be scared to do anything — to call relatives, to send money back — for fear of being wrongly suspected.”

As residents waited anxiously for answers, with some repeatedly checking Kenyan news outlets for names of the attackers, the federal authorities in Minnesota said they were continuing to investigate the Shabab’s recruiting of young men, known as “the travelers,” but provided few new details. “We’ve had an ongoing investigation into the travelers since 2007, and it continues to this day,” said Kyle Loven, a spokesman for the F.B.I. office in Minnesota.

A senior American official in Washington said F.B.I. field offices in Minneapolis; San Diego; Columbus, Ohio; and other cities with large Somali populations were reviewing “high profile” cases involving young Somali men who had drawn attention for possible extremist views. Since the siege in Nairobi, officials from the Department of Homeland Security, who set up community outreach programs with Somali-American communities after 2007, have increased their activities.

“We’ve ramped up our efforts,” said the official, who spoke on the condition of anonymity because of the continuing investigation. “We’re obviously interested in any information about young men in their community who are unaccounted for and might be caught up in this.”

In Minneapolis neighborhoods like Cedar-Riverside, with a large Somali population, residents expressed a mix of sometimes clashing emotions: worry at the prospect of more recruiting, but also anger over the uncertainty of the claims and a sense that an entire group was being tainted by the acts of a few troubled men.

Some dismissed the claims of any ties to the mall attack as absurd and overblown. “Where are the names?” Halima Yusuf, a Minneapolis resident, said on Friday. “Where are the photographs?”

But others seemed less certain, saying the earlier episodes of recruiting left them wondering and worrying.

“Everybody is praying and hoping that they will not be from here,” said Sadik Warfa, a community activist whose office is in a large mall of Somali shops that sell tea, haircuts, handmade gowns, phones, pastries and more. Three flags line his walls: those of the United States, Somalia and Minnesota.

“We don’t want our neighbors to think this about us,” Mr. Warfa said. “We want the people to know that we feel the same way all Americans do: that this is terrible and that Minnesota is not a hotbed for terrorism. How could a kid who grew up here with ice cream and hamburgers and football — how could this happen?”

More than 32,000 people of Somali ancestry live in Minnesota, census figures show, and local leaders say the true number is far higher. Some came in the 1990s after fleeing civil war, and others are their children, many of them born in this country.

The recruiting by the Shabab, which means “youth,” began in the area in 2007, the authorities have said, as young Somali-Americans were encouraged in secret gatherings to go train in Somali camps. At the time, the authorities said, they thought they would be fighting Ethiopian troops who had entered Somalia a year before and were seen by some in the Somali diaspora as unwanted interlopers.

Since then, residents said, views have hardened against the Shabab. Some of the recruits have died in violence. And as people tied to recruiting and raising money have been prosecuted, any such efforts, young Somalis said, seemed to have shifted largely to the Internet and videos.

“When it happens once, you are surprised,” said Abdi Ismail Samatar, a professor at the University of Minnesota. “When it happens a second time, you have to say, ‘What could we have done?’ And that’s what people are asking themselves.”

Still, even as religious leaders condemned the violence in Kenya, not all seemed sure of what vulnerable young adults — some who have lived with single mothers in impoverished conditions here — were thinking. “These kids are like any American young people,” Ahmed Burale, an imam, said through an interpreter after completing prayers. “If they want your advice, you can teach them.”

On Friday, a group of Somali-Americans gathered in a park. Some women held signs that read “Prosecute all Al Shabab recruits” and “We are good Americans.”

Ahmed Baraki rose to a microphone, calling for a moment of silence to stand in solidarity against the suffering at the mall in Kenya.

“We are loyal Minnesotans,” he said.