Police said a man wearing a private security firm uniform stabbed at least eight people at a shopping mall in the northern U.S. state of Minnesota.
The September 17 attack in the city of St. Cloud ended with the suspected attacker being shot dead by an off-duty police officer.
The assailant "made some references to Allah,” St. Cloud police chief Blair Anderson said.
"We have confirmed that he asked at least one person if they were Muslim before he assaulted them," Anderson told reporters.
He declined to describe the attacks as an act of terrorism, but FBI Special Agent-in-Charge Rick Thornton said later that it was being investigated as a possible act of terrorism. He said agents were still digging into the attacker's background and possible motives.
An Islamic State-run news agency claimed that the attacker was a "soldier of the Islamic State" who had heeded the group's calls for attacks.
It was not immediately clear if the group had planned the attack or even knew about it beforehand.
Islamic State militants have encouraged so-called "lone wolf" attacks and also claimed past attacks that are not believed to have been planned by its central leadership.
St. Cloud is about 113 kilometers northwest of Minneapolis, the largest city in Minnesota.
Based on reporting by AFP and AP