US homeland security chief Jeh Johnson warned shoppers in one of America's biggest malls to be on their guard Sunday after an Islamic militant group posted a video calling for attacks on western malls.
The warning comes as the US and other nations are increasingly jittery about the threat of "lone wolf" attacks carried out by radicalized people in their home country.
"I would say that if anyone is planning to go to the Mall of America today, they've got to be particularly careful," Johnson said on CNN's "State of the Union."
The al Qaeda-linked Shebab insurgent group also threatened Canada's massive West Edmonton Mall, London's famous Oxford Street shopping hub and two malls in France: Le Forum des Halles and Les Quatre Temps.
A US administration official said, however, there was "no indication of a specific, credible threat to the US."
But attacks in Paris, Copenhagen and Ottawa by homegrown extremists have set security officials on edge, and prompted Washington to sponsor a security summit earlier this week to discuss the threat.
Shebab carried out a bloody attack and takeover of a mall in Nairobi in September 2013 that killed at least 67 people.
In a video distributed on Twitter Saturday, the group ran a documentary-style account of the Kenya attack. It was followed by an appearance by a masked fighter who suggested similar attacks could be carried out on other malls in the United States, Canada, Britain and France.
"If just a handful of mujahideen fighters could bring Kenya to a complete stand-still for nearly a week, just imagine what the dedicated mujahideen could do in the West to American or Jewish shopping centers across the world," the militant said.
"What if such an attack were to occur in the Mall of America in Minnesota? Or the West Edmonton Mall in Canada? Or in London's Oxford Street?" he said.
The video was picked up by SITE, a group that monitors jihadist websites.
The Mall of America, located in Minnesota and reputedly the country's largest with 40 million visitors a year, said it had taken extra security measures in response to the threat by the Shebab, a Somalia-based insurgent group.
"Enhanced security measures to include additional personnel have been implemented and all information is being monitored," said the police department for Bloomington, the Minneapolis-St Paul suburb where the shopping center is located.
"At this time, there is no credible threat associated with Mall of America," it said, adding that the facility was a "very safe place."
Johnson said the threat was indicative of a new type of homegrown threat and requires careful tracking of people suspected of supporting militant groups.
"This latest statement from al-Shebab reflects the new phase we've evolved to in the global terrorist threat in that you have groups such as al-Shebab, ISIL, publicly calling for independent actors in their homelands to carry out attacks," said Johnson, who is the US secretary of homeland security.
"We're beyond the phase now where these groups would send foreign operatives into countries after being trained someplace," he added.
Johnson said the government has to take it seriously any time a group calls for an attack against a specific place, but he did not say if his department had other specific information about the threat.
The Department of Homeland Security is in the middle of a funding battle between President Barack Obama and the Republican-controlled Congress.
Lawmakers have funded all federal departments until the end of the 2015 fiscal year, except for DHS, held up by a Republican attempt to override Obama's decision to defer deportations of millions of undocumented immigrants.
In his appearances on Sunday television shows, Johnson brought up the funding battle in context of the most recent mall threat.
"It's all the more reason why I need a budget," Johnson said.
The department may have to furlough 30,000 people if it doesn't receive funding by the end of the week, and a "skeleton" staff hampers the ability to detect threats, Johnson said.
"It's absurd that we're even having this conversation about Congress' inability to fund homeland security in these challenging times."