The U.S. homeland security chief said authorities are taking seriously a threat made by Somali-based Islamist militants against Western shopping malls.

Homeland Security Secretary Jeh Johnson was reacting to a video released by al-Shabab terrorists, appearing to call for attacks on shopping areas.  

Speaking Sunday, Johnson said the global terrorist threat has evolved to militant groups "publicly calling for independent actors in their homelands to carry out attacks." 

He said, "We're beyond the phase now where these groups would send foreign operatives into countries after being trained some place [else]."

US, Canada, Britain mentioned

Al-Shabab claimed responsibility for a September 2013 attack that killed 67 people at the Westgate shopping mall in Nairobi, Kenya.

The terrorist threat specifically mentioned shopping areas in the United States, Canada and Britain.

Among them was the Mall of America, in the northern U.S. state of Minnesota. The area is home to a sizeable Somali immigrant population.  

U.S. law enforcement officials have been concerned about the potential for radicalization among members of immigrant communities.  

A Minnesota man was indicted last week on charges of conspiring to support the Islamic State extremist group and lying to federal agents investigating recruitment by militant groups.

Prosecutors said dozens of people from Minnesota, many of them Somali-Americans, have traveled or attempted to travel overseas to support groups such as Islamic State or al-Shabab since 2007.