Canadian Prime Minister Justin Trudeau on Tuesday denounced the killing of four Muslim family members, run down by the driver of a pick-up truck, as a hate-driven "terrorist attack," and urged the nation to stand up against intolerance.
He also promised to redouble efforts to fight far-right groups.
The victims -- a husband and wife, their teenage daughter and the child's grandmother -- were killed Sunday when the truck mounted a curb and struck them in the city of London, in Canada's central Ontario province.
The couple's nine-year-old son, orphaned in what police said was a planned attack targeting a Muslim family, was recovering in hospital from serious injuries.
"This killing was no accident. This was a terrorist attack, motivated by hatred, in the heart of one of our communities," Trudeau said during an impassioned speech at the House of Commons.
The Canadian leader later addressed an outdoor vigil of thousands at the mosque the family attended, speaking directly to the country's Muslim community.
"You are not alone. All Canadians mourn with you, and stand with you tonight," he said at the vigil, which was attended by all of the country's political leaders.
He said Canada was "not immune" to the rising discrimination and division witnessed elsewhere in the world in recent years.
"Together, we can counter this darkness, and this intolerance," he said.
The victims of Sunday's attack have been identified as Madiha Salman, age 44, who had done post-graduate work in civil and environmental engineering; her husband, Salman Afzaal, age 46; their 15-year-old daughter, Yumna Salman; and a woman reported to be Afzaal's 74-year-old mother, who was not named.
Canada's long reputation for tolerance has been bruised in recent years amid a series of hate and race-based crimes starting with a 2017 shooting at a Quebec City mosque that claimed six lives.
The country's Muslim population, just three percent of the total, has been left feeling increasingly vulnerable. Several Muslim organizations have demanded action to curb far-right extremist groups.
The suspect, identified as 20-year-old Nathaniel Veltman, was arrested at a mall seven kilometers away from the site of Sunday's attack, said Detective Superintendent Paul Waight.
Veltman has been charged with four counts of first-degree murder and one count of attempted murder.
"They were all targeted because of their Muslim faith," Trudeau said, promising to step up the country's fight against far-right racist groups. "This is happening here, in Canada. And it has to stop."
Party leaders in the House of Commons condemned the violence as an act of "Islamophobia."
"The reality is, our Canada is a place of racism, of violence, of genocide of indigenous people," said Jagmeet Singh, leader of the New Democrats.