EDMONTON - Canadian police arrested a suspect in violent, Saturday night attacks in Edmonton that injured a traffic officer and four others, describing the incidents as "acts of terrorism."A man struck an officer directing traffic outside a football stadium with his vehicle, stabbed him and then fled. Police arrested a suspect several hours later after a car chase in which four pedestrians were hit.Authorities believe the man acted alone, although they have not ruled out the possibility that others were involved, Edmonton Police Service Chief Rod Knecht said at a Sunday morning news conference.Police found a flag of the Islamic State militant group inside the car that struck the traffic officer, Canadian broadcasters CBC and CTV reported.US national security agencies are looking into the case and have yet to determine whether the attacker was working with others, including Islamic State, or if he was a "lone wolf," a US official told Reuters.Victims were taken to the hospital for treatment, and the officer's condition was not critical, Knecht said. Details on the condition of the other victims were not immediately available.Police released a graphic video that showed the attack on the officer, and they asked the public to call with any information that would help them with the case.Canadian Prime Minister Justin Trudeau said federal authorities were working with local police.“While the investigation continues, early reports indicate that this is another example of the hate that we must remain ever vigilant against," he said in a statement.Canadian Public Safety Minister Ralph Goodale tweeted that the country "will not be intimidated by terrorist violence." Its terror threat level remained at medium, where it has been since late 2014.Police said the suspect, believed to be 30, crashed the car through a barricade and hit the officer at about 8:15 p.m. local time, sending him flying 15 feet into the air and against a police cruiser. The suspect then jumped out of the car, stabbed the officer and fled on foot.Later that evening, police at a checkpoint identified a man driving a U-Haul vehicle as the car's owner.The suspect fled and intentionally hit pedestrians on a crowded downtown street as police pursued him, sending at least four people to the hospital with injuries, Knecht said.Police arrested the suspect after the vehicle flipped over during the pursuit."We ask that our citizens remain vigilant and observant of their surroundings, and contact police should they notice any other unusual activities around the city," they said in the statement.Canada has not experienced as much violence from extremist attacks as the United States and Western European nations, but there have been several deadly incidents in recent years.In January, a French-Canadian university student was charged with murder after six people were shot and killed inside a Quebec City mosque, in what Trudeau called “a terrorist attack.”In August 2016, Canadian police raided an Ontario home and killed Aaron Driver, who they said was an Islamic State supporter preparing an attack on a Canadian city with a homemade bomb.In 2014, Canada was stunned by two deadly attacks that police said were the work of homegrown radicals and led to tougher new anti-terrorism measures.A gunman killed a soldier at Ottawa’s national war memorial before launching an attack on the Canadian Parliament in October 2014. In the same week, a man ran down two soldiers in Quebec, killing one.