Washington (CNN) Shoppers at the Mall of America need to be "particularly careful" after a terror group singled out the Minnesota super-mall for attacks, Homeland Security Secretary Jeh Johnson says.

During an interview Sunday with CNN "State of the Union" host Gloria Borger, he cautioned shoppers who plan to visit the mall that Al-Shabaab included on a list of targets in a video released this weekend.

"If anyone is planning to go to the Mall of America today, they've got to be particularly careful," Johnson said. "There will be enhanced security there, but public vigilance, public awareness and public caution in situations like this is particularly important, and it's the environment we're in, frankly."

His comments come as the Mall of America implements new security measures -- some of which the mall said in a statement would be noticeable to shoppers.

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