A man who wounded eight people in a knife attack on Saturday at a mall in central Minnesota before he was shot dead by an off-duty police officer is a "soldier of the Islamic State," the militant group's news agency said.

The man, who was wearing a private security uniform, made references to Allah and asked at least one person if they were Muslim before he assaulted them at the Crossroads Center mall in St. Cloud, the city's Police Chief William Blair Anderson told reporters.

Reuters was not immediately able to verify the authenticity of the claim made by Islamic State through the group's affiliated Amaq news agency.

A spokesperson for the U.S. National Security Council said it was aware of the claim but deferred to local investigators. The FBI did not immediately respond when asked about the Amaq statement.

"Whether that was a terrorist attack or not, I'm not willing to say that right now because we just don't know," Anderson said at a news conference.

"We'll figure out what this is and when we do we will be transparent about it," he added. He gave no details of the identities of the victims.

The knife attack in St. Cloud, a community about 60 miles (100 km) northwest of Minneapolis-St. Paul, comes at a time of heightened concern in the United States about the threat of violence in public places.

An explosion rocked New York City's bustling Chelsea district on Saturday, injuring 29 people in what authorities described as a deliberate, criminal act. But both New York Governor Andrew Cuomo and New York City Mayor Bill de Blasio said there was no indication it was linked to international terrorism.

In St. Cloud, the attacker entered the mall in the evening as it was busy with shoppers, Anderson said.

He attacked his victims at several sites in the shopping center, which will remained closed on Sunday as police investigate, the police chief said.

The eight wounded were transported to St. Cloud Hospital but none were believed to have life-threatening injuries, said Chris Nelson, a communications specialist for the medical facility.

One victim was expected to remain there, but the other seven patients had already been released or were expected to be let go shortly, officials said.

Police officials said they were still interviewing witnesses hours after the attack.

The off-duty police officer who shot the suspect was from a jurisdiction outside of St. Cloud, Anderson said. He would not say which agency employs the officer.