(CNN) - There's a terror threat on U.S. soil.
Somalia-based Al-Shabaab released a video on Saturday calling for attacks on malls in the U.S., Canada and the United Kingdom.
Among others, the Mall of America in Minnesota and the West Edmonton Mall in Alberta, Canada, were named.
U.S. officials say Americans should be vigilant.
"We take this kind of thing very seriously," Homeland Security Secretary Jeh Johnson said.
U.S. officials say there is no "specific, real threat" against shopping malls in the U.S., but Johnson warns Americans to be careful.
"What we're telling the public in general, is you've got to be vigilant. ... If anyone is planning on going to the Mall of America today, they've got to be particularly careful," he said.
In a statement, the Mall of America said it is ramping up security: "Mall of America is aware of a threatening video that was released which included a mention and images of the mall. We take any potential threat seriously and respond appropriately. We have implemented extra security precautions. Some may be noticeable to guests, and others won't be."
Al-Shabaab is responsible for a 2013 deadly attack at a Kenyan shopping mall. More than 60 people were killed as the terrorists besieged the retail center in Nairobi.
Johnson says the video indicates a new phase in terrorism threats: terrorist groups publicly calling for people to launch attacks in their homelands.
"I am very concerned about the serious potential threat of independent actors here in the United States," he said.
U.S. law enforcement officials say the FBI is working with malls across the country to improve security.
Later Sunday, Johnson told a national governor's association meeting that full funding for the DHS is imperative to fight terrorist groups like Al-Shabaab.
Funding for the department will run out if Congress does not pass a spending bill by Saturday.
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