Canadian authorities say two incidents in Edmonton are being investigated as acts of terrorism after a man struck a police officer with a car before stabbing him and later plowed a truck into pedestrians on a busy street, injuring at least four people.

In a Sunday afternoon press conference, authorities said the suspect is a male Somali national and refugee who was previously known to Edmonton police and the Royal Canadian Mounted Police (RCMP).

Police have arrested the suspect for several offenses, including participation in a terrorist act and the commission of an offense for a terrorist group, said Chief Rod Knecht of the Edmonton Police Service.

The suspect was investigated in 2015 after police received a complaint he was “espousing extremist ideology,” said RCMP Deputy Criminal Operations Officer Marlin Degrand, but there was insufficient evidence to pursue terrorism charges. The suspect was not deemed to be a threat at the time, Degrand said.

Formal charges have not been filed against the suspect, who police believe acted alone. Police had not released his name as of late Sunday afternoon.

The first incident happened Saturday at 8:15 p.m. (10:15 p.m. ET) when the driver of a white Chevrolet Malibu drove it into a traffic barricade. Police had set up the roadblock near Commonwealth Stadium for an Edmonton Eskimos football game.

A man drove the car at high speed, striking the police officer who had been standing between a traffic barricade and his cruiser.

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