(CNN) After a siege at a Kenyan mall two years ago, the FBI started staging mock attacks in U.S. shopping centers during off hours to test their readiness, an official said.

More than 60 people died when Al-Shabaab militants raided an upscale mall in Nairobi and held shoppers hostage for four days.

The terror group released a video Saturday calling for similar attacks in malls in the United States, Canada and the UK.

Although Homeland Security and the FBI say they are not aware of a specific, credible plot against U.S. malls, they've worked to improve security in light of the attack in Kenya.

Last year, the FBI teamed up with various malls nationwide to increase preparedness, a law enforcement official told CNN. It tested the readiness of SWAT teams by staging fake attacks at malls when they were closed, the official said.

Since then, the FBI has had a program that works with malls to improve security, the official said.

Competing for attention

The Somalia-based terror group has limited past attacks to its home country and neighboring Kenya and Uganda.

But as other terror groups such as ISIS have made vicious headlines, Al-Shabaab may be feeling left out, U.S. officials said.

The Department of Homeland Security and the FBI say they believe the video was the militants' attempt to compete for attention and recruits with other terrorist groups, one official said.

Al-Shabaab's strength is compromised, a U.S. law enforcement official said, and while the group has the desire to see a mall attack in the U.S., it probably isn't able to do so.

Caution urged, nonetheless

Despite what some officials described as an attention ploy, security was beefed up in malls listed as potential targets.

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Homeland Security Secretary Jeh Johnson said there's no credible evidence suggesting a U.S. mall attack is in the works. But shoppers should be vigilant nonetheless, he said.

"There will be enhanced security (at malls)," he said Sunday. "But public vigilance, public awareness and public caution in situations like this is particularly important, and it's the environment we're in, frankly."

Stressing that there is no known credible threat to any mall, Johnson cautioned that attacks can be unpredictable.

"I won't know about when the next bad actor is going to strike," he said.

'We take any potential threat seriously'

In Bloomington, Minnesota, home to Mall of America, one of the shopping centers named in the video, law enforcement agencies said they remain vigilant.

"Enhanced security measures to include additional personnel have been implemented and all information is being monitored," local police said in a statement Sunday.

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The mall said it takes any "potential threat seriously" and has implemented extra security.

"We have protocols in place that as things happen we can ramp up and we've implemented some of those strategies," said Bloomington Police Chief Jeff Potts. "Some of them are things that people wouldn't notice."

Michael Rozin, a security consultant to the Mall of America, said that dedicated explosive-detection dog teams patrol the mall. Officers are trained specifically in behavior-detection techniques, he said.

The mall also has its own intelligence branch and a station where teams monitor chatter on social media, according to Rozin.

The West Edmonton Mall in Alberta, Canada, which was also named in the video, said it has boosted security and is working with federal and local law enforcement agencies.

"Canada will not be intimidated by threats from any terrorist organization," Public Safety Minister Steven Blaney said.

The video also mentioned shopping centers in the UK.

Westfield Corp. said there is no "evidence of an imminent threat" to its shopping centers, but it's taking steps to ensure safety.

UK Metropolitan Police Counter Terror Command also said it is aware of the video.

Reaction from the Somali community

Amano Dube, a leader in the Somali community in Minneapolis, said radicalization is a great concern.

"The root cause of the problem is poverty, identity crisis and a lack of education," he told CNN. "We have to create projects and programs and opportunities for these young men to focus on the future and positive life-changing things."

The Somali community has met to discuss the video and to address it in a unified manner, he said, likening radicalization to a disease.

"We have to work hard for our community and families, to dismantle this; it's a grave concern," Dube said. "With social media ... it has really given the best opportunities for this evil to affect all communities and ages."

Al-Shabaab's previous targets

Although Al-Shabaab's past attacks have been limited to East Africa, the militants have heavily recruited in Minneapolis, where young men have been slipping away to join the terror group. The city is home to the largest Somali population in the United States.

As the attacks get more daring, the international community has rallied to fight the militants.

Last year, a U.S. airstrike in Somalia killed the Al-Shabaab leader. The terror group later replaced him and vowed to avenge his death.

Al-Shabaab started off with a goal of waging a war against the Somali government in an effort to implement a stricter form of Islamic law, or Sharia.

It has since shifted focus to terrorist attacks in Somalia and beyond.