A car and knife attack on a police officer and a high-speed chase of a moving van that left four people injured appear to be the work of a "lone wolf", Canadian authorities said.
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.
Police added that the suspect was a Somali refugee who was known to authorities.
Marlin Degrand, assistant commissioner of the Royal Canadian Mounted Police said the suspect was flagged in 2015 for extremist ideologies, but following police interviews he was not charged with any offences.
They continued that pending charges include terrorism and five counts of attempted murder.
Mr Knecht said a so-called Islamic State group flag was found in the car that hit the officer, and Canadian Prime Minister Justin Trudeau called it a terror attack.
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 was sent flying in the air while the Malibu crashes into the police car.
The driver then gets out and appears to stab the officer, who wrestles the suspect to the ground and then gets back up as the suspect flees on foot.
"Seeing the video is very upsetting because of the level of violence and level of intent," Mr Iveson said.
Mr Knecht said the suspect fled on foot after stabbing the officer.
The injured man was named as Constable Mike Chernyk.
Mr Chernyk was released from hospital overnight with stab wounds to his head and cuts to his arms.
Several hours after the attack, a U-Haul van was stopped at a checkpoint in the city.
Mr Knecht said the name of the driver was similar to the name of the registered owner of the car that hit the officer.
He continued that the van then sped off toward downtown with police cars in pursuit, swerving at pedestrians at crosswalks throughout the chase.
Four people were injured, at least one of who remains in hospital in a stable condition.
The van eventually flipped over the suspect was arrested after being tasered.
"It is believed at this time that these two incidents are related," Mr Knecht said of the attack and vehicle chase.
"It was determined that these incidents are being investigated as acts of terrorism."
Mr Knecht said Edmonton police were working with the Royal Canadian Mounted Police's national security enforcement team and other Canadian security agencies.
Mr 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."
He advised the public to remain vigilant and observant of their surroundings.
The terror threat level remains at "medium" in Canada.