Per ABC News:

The FBI is looking at the stabbing attack at a mall in St. Cloud, Minnesota, as possible terrorism, authorities said Saturday, as ISIS claims responsibility for the violence that left nine people injured.
“We are currently investigating this as a potential act of terrorism, and I do say ‘potential,’” said FBI agent Richard Thornton of the bureau’s Minneapolis office at a Saturday press conference.
Thompson said investigators are looking at all aspects of the life of the suspect, who has yet to be identified and who was shot and killed at the scene by an off-duty police officer, to determine his motives and whether there is a link to terrorism.
“We will try to peel back the onion to find out what motivated this individual to commit the horrific act that he did,” Thornton said.
ISIS has claimed responsibility for the attack by the man, who was wearing a security guard’s uniform when he stabbed people at the mall at about 8 p.m. on Saturday night.
The attacker was “a soldier of the Islamic State” who carried out the attack in response to ISIS calls for violence against civilians, according to a news agency, Rasd, operated by the Islamic State group.