WASHINGTON - The head of US homeland security urged vigilance after Somali-based militants called for attacks on shopping centres in the US, Canada and Britain.
Visitors to the Mall of America in the northern US state of Minnesota should be "particularly careful," said the Department of Homeland Security Secretary Jeh Johnson.
Speaking on morning talk shows in the US, Johnson called the video "the new phase" of the global terrorist threat and warned the public to be vigilant.
"I am very concerned about serious potential threats of independent actors here in the United States," said Johnson. "We've seen this now in Europe, we've seen this in Canada."
"These groups are relying more and more on independent actors to become inspired, drawn to the cause and they'll attack on their own," Johnson said, speaking on CNN's Sunday morning interview show, State of the Union.
The masked narrator called on Muslims to attack shopping malls, specifically naming the Mall of America in Minnesota, the West Edmonton Mall in Canada and the Westfield mall in Stratford, England.
However, Johnson said that authorities had no concrete intelligence of a pending attack, and the Homeland Security Department later told CNN there was no reason not to visit the mall.
Actual mall shoppers put aside the terrorists' threat.
In Kenya, the government dismissed the al-Shabab video as "cheap propaganda".
"They're using propaganda to legitimise what cannot be legitimised. When you lead a group to go and attack a shopping mall and kill innocent shoppers that cannot be legitimised, those were not soldiers," Interior Ministry spokesman Mwenda Njoka said.
"Muslims also died in the Westgate attack. It's in our interest to ensure Somalia is stabilised because the instability affects us. The video is cheap propaganda trying to re-write history and to get more support from those support them."
Asked about the specific threat against the Mall of America, Johnson said: "Any time a terrorist organisation calls for an attack on a specific place we've got to take that seriously. What we're telling the public is you've got to be vigilant... There will be enhanced security there that will be apparent, but public vigilance, public awareness and public caution in situations like this is particularly important. It's the environment we're in."
The Mall of America, one of the nation's largest, located in Bloomington, Minnesota - just outside Minneapolis - said in a statement that it was "aware of a threatening video which includes a mention and images of the mall," and said extra security had been put in place
Shoppers seemed undeterred Sunday by the threat. In Kenya, the government dismissed the al-Shabab video.
"I'm more afraid of the cold today than any terrorists," said Mary Lamminen, of St. Paul.
David Modrynski said he talked with his wife and son about whether to visit the mall after hearing about the video. "But we can't stop living our lives because somebody says they're going to do something," Modrynski said.
The US state of Minnesota is home to the largest Somali population in the country, has has been the target of terror recruiters. Since 2007, more than 22 young Somali men from Minnesota have traveled to Somalia to join al-Shabab, and a handful of Minnesota residents have also traveled to Syria to fight with militant groups within the last year, authorities say.
At least one man from Minnesota has died while fighting for the Islamic State group.
On Thursday, a 19-year-old Minneapolis man who was stopped at a New York City airport in November as he and three others were allegedly attempting to travel to Syria was indicted on charges associated with supporting the Islamic State group.
Hours after the threat to bomb, traffic and shopping levels at the West Edmonton Mall in Canada appeared normal.