EDMONTON, Alberta >> A car and knife attack on a police officer outside a football game and a high-speed chase of a moving van that left four people injured appear to be the work of a single suspected terrorist, Canadian authorities said today.

Edmonton Police Chief Rod Knecht said officers took the suspect, later described as a 30-year-old Edmonton man, into custody and he is believed to have acted alone. Knecht said an Islamic State group flag was found in the car that hit the officer, and Canadian Prime Minister Justin Trudeau called it a terror attack.

“To the best of our knowledge, this was a lone wolf attack,” Edmonton Mayor Don Iveson said.

The incident took place outside a Canadian Football League game at Edmonton’s Commonwealth Stadium on Saturday night.

Police released video showing a white Chevrolet Malibu ramming into a police officer standing in front of his cruiser. The officer is sent flying in the air while the Malibu crashes into the police car. The driver then gets out and appears to stab the officer.

“Seeing the video is very upsetting because of the level of violence and level of intent,” Iveson said.

Knecht said the suspect fled on foot after stabbing the officer.

The officer was taken to a hospital and treated for non-life-threatening injuries while a manhunt was launched, and Knecht said his condition was “not critical.”

A few hours later, a U-Haul van was stopped at an impaired driving checkpoint north of downtown, on Wayne Gretzky Drive. Knecht said the name of the driver was similar to the name of the registered owner of the car that hit the officer.

He said the van then sped off toward downtown with police in pursuit.

Police say the vehicle swerved at pedestrians at crosswalks throughout the chase. Four people were hurt, but the extent of their injuries was not immediately known.

The van eventually flipped near a downtown hotel and the suspect was arrested. Knecht said the man was known to police but did not release his name.

“It is believed at this time that these two incidents are related,” Knecht said. “It was determined that these incidents are being investigated as acts of terrorism.”

Knecht said Edmonton police were working with the Royal Canadian Mounted Police’s National Security Enforcement Team and other Canadian security agencies. He advised the public to remain vigilant and observant of their surroundings.

Witness Pat Hannigan told reporters he saw police pull a man from the windshield of the toppled van and estimated that 30 police cars had been chasing it.

Austin Elgie, manager of The Pint bar just west of the downtown core, also saw the van zoom by with police giving chase.

It “peeled” into an alley where people were smoking, he said.

“It was crazy,” Elgie said. “It just came around the corner, ripping. I thought at first he was pulling over for the cops coming by, but he was clearly the one they were chasing.”

Elgie said the van hit a man who was a bar customer.

“I have a registered nurse on my bar team, and I grabbed her and had her look after the guy until the ambulance came,” he said. “He was breathing and we got him in the ambulance and he was still breathing.”

It was military appreciation night at the football game between the Edmonton Eskimos and the Winnipeg Blue Bombers. Canada’s chief of defense staff, Gen. Jonathan Vance, conducted the pregame coin flip and two CF-18 fighter jets did a fly-past before kickoff. More than 800 Boy Scouts were expected at the game.

Trudeau said in a statement that Canadians “stand with the people of Edmonton after the terrorist attack on Saturday that sent an Edmonton Police Service officer to hospital and injured a number of innocent people who were out to cheer on their football team and to enjoy an evening in their city.”

“We cannot — and will not — let violent extremism take root in our communities. We know that Canada’s strength comes from our diversity, and we will not be cowed by those who seek to divide us or promote fear,” Trudeau said.

A Public Safety Department spokesman said the national terrorism threat level for Canada remains at “medium,” where it has stood since the week a gunman stormed Parliament in Ottawa in fall 2014. The man killed a soldier at the national war memorial before being shot dead inside Parliament.

In France today, a man with a knife attacked people at the main train station in the southeastern city of Marseille, killing two women before being fatally shot by soldiers, officials said.