Shopping malls across the United States are on high security alert and reinforcing protection measures Monday after Somalia-based terror group al-Shabaab sent out a video encouraging such attacks, most notably directed at the Mall of America.

According to Martha C. White of NBC News, the Somali terror group, urged radicals in a video to conduct "lone-wolf" attacks on shopping centers in the U.S., Canada and United Kingdom. Al-Shabaab singled out the Mall of America as a prime target; it is located in the Minneapolis metro region, which has the largest Somali-American community in the country.

"We are kind of in uncharted territory on this one," Garrick Brown, a regional vice president of research at real estate services company DTZ, said. "[Terror groups] putting a call out to encourage American lone gunman types is something that we don't have a good gauge on."

NBC News reported that al-Shabab previously attacked malls before. It claimed responsibility for the 2013 attack at Westgate Mall in Nairobi Kenya, which left dozens dead.

"If just a handful of mujahedin fighters could bring Kenya to a complete standstill for nearly a week, imagine what a dedicated mujahedin in the West could do to the American or Jewish-owned shopping centers across the world," an unidentified man said on the video. "What if such an attack was to occur in the Mall of America in Minnesota?"

As for the threatened mall itself, William M. Welch and John Bacon of USA Today reported that the Mall of America, through its law-enforcement agencies, said that it saw "no credible threat" in the video, but has decided to implement "extra security precautions."

Westfield Corp., which operates 38 malls across the U.S. and more overseas, told USA Today that it saw "no evidence of an imminent threat" against any of its properties. However, the company stated that it "will take every available step to keep our shopping centers safe."

Homeland Security Secretary Jeh Johnson told NBC's "Meet the Press" that Americans should be "particularly vigilant" and aware of their surroundings.

"I am not telling people to not go to the mall," Johnson said.

Brown told NBC News that despite the latest threats, shopping habits in the U.S. probably won't change much.

"I think they might see a small decline in traffic today, tomorrow and maybe over the next few days," Brown predicted. "But so long as nothing actually happens I don't think that the decline in traffic will be much or long."

NBC News reported that malls would have to strike a balance between securing their centers and minimizing consumer inconvenience due to heightened security measures. While hiring extra security staff and searching delivery trucks can work behind the scenes, other measures, such as the use of metal detectors, may scare off some people.

"It's a known fact that people value their time," Tom LaTourrette, a physical scientist at Rand Corp., said. "Most security involves lines. That's one of the most common problems."