Canadian police are questioning the suspected driver of a rented van that ploughed into pedestrians in northern Toronto on Monday, killing 10 and injuring 15.
Alek Minassian, 25, was not previously known to authorities, police said.
The incident appeared to be deliberate but the motive was not clear, officials added.
Canadian Prime Minister Justin Trudeau said the “tragic and senseless attack” had brought him “great sadness”.
Meanwhile, an officer has been praised for not opening fire during a tense standoff with the suspect, who claimed to be armed.
Video broadcast on CBC News showed a man pointing what appeared to be a gun at officers and shouting “kill me”.
The officer tells the man to “get down” and when the suspect says he has a gun, the officer repeats: “I don’t care. Get down.” The suspect was then arrested without shots being fired.
How did the incident unfold?
Police said the white rental van mounted the kerb on Yonge Street between Finch Avenue and Sheppard Avenue at about 13:30 local time (17:30 GMT) on Monday and drove into pedestrians along a 2km (1.24 mile) stretch.
Reza Hashemi, who owns a video shop on Yonge Street, told the BBC he heard screaming on the other side of the road.
He said the van was repeatedly mounting the pavement and running into people.
One witness told City News that the driver was “hitting anything that comes in the way”.
“People, fire hydrants, there’s mail boxes being run over,” said the unnamed man, who said he was driving behind the van during the incident.
As the van continued, the man said he sounded his horn to try to warn pedestrians. “I witnessed at least six, seven people being hit and flying in the air, like killed, on the street,” he said.
Pictures from the scene showed bodies covered in orange sheets along the van’s route. Debris and items of clothing were scattered across the pavements and road.
The van was brought to a halt by police several streets away and was quickly surrounded.
What is known of the suspect?
Very few details have been released about the man being questioned.
Police said Alek Minassian was from the northern Toronto suburb of Richmond Hill.
Toronto Police Chief Mark Saunders told a news conference that he was not previously known to authorities.
“The actions definitely looked deliberate,” he said, adding that it was too early in the investigation to say whether the incident was terror-related.
“We don’t rule out anything. What we have to do is to follow what we have because it’s very early in the investigation,” he said.
Standing alongside him, Canadian public safety minister Ralph Goodale said there “would appear to be no national security connections”.
Canadian broadcaster CBC, citing government officials, said Mr Minassian was not associated with any known terror groups.
What else is known?
Van rental company Ryder System Inc confirmed that one of its vehicles was involved and said it was co-operating with authorities.
The incident happened while foreign ministers of the G7 leading industrialised nations – Canada, US, Britain, France, Germany, Italy and Japan – were holding talks in Toronto.
Canadian Foreign Minister Chrystia Freeland said the G7 meetings would continue on Tuesday as planned.