Man accused of Toronto van attack posted 'cryptic' message minutes earlier.

The man accused of ploughing a rental van into pedestrians on a crowded Toronto footpath, killing 10 people in Canada’s deadliest mass killing in decades, left a “cryptic message” on social media before the attack, police say.

Suspect Alek Minassian, 25, was charged with 10 counts of murder and 13 counts of attempted murder following Monday’s incident.

One possible clue to his motive emerged as Facebook confirmed Minassian wrote a post before the incident that referenced an “incel rebellion.”

The term is shorthand used in some online message boards for “involuntary celibacy”, a loose social media movement of men who blame women for their celibacy.

Canadian authorities have declined to say whether anger toward women had motivated the attack.

The post also voiced admiration for a man who killed six college students before taking his own life in California in 2014 and who cited the “cruelness of women” for his virgin status.

“The accused is alleged to have posted a cryptic message on Facebook minutes before” the attack, Graham Gibson, a Toronto police detective sergeant, told a news conference. The majority of the victims were women, ranging in age from their mid-20s to early 80s, Gibson said.

He said the question of whether the attack was driven by anger against women was “going to be part of our investigation.”

Facebook has since deleted Minassian’s account, a representative said. “There is absolutely no place on our platform for people who commit such horrendous acts,” she said in an email.

Minassian kept his shaved head down during a brief court appearance in Canada’s largest city, speaking quietly with a defence lawyer and stating his name in a steady voice when asked to do so.

The incident had the hallmarks of deadly vehicle assaults by Islamic State supporters. Prime Minister Justin Trudeau said there was no reason to suspect any national security connection.

Trudeau called on all Canadians to stand united with Toronto as flowers and scrawled messages in multiple languages piled up at a makeshift memorial in the city's north end, an ethnically diverse neighbourhood of office buildings, shops, restaurants and homes.

"We cannot as Canadians choose to live in fear every single day as we go about our daily business," Trudeau told reporters outside parliament in Ottawa.

Minassian had briefly served in Canada's armed forces in late 2017 but asked to be voluntarily released after 16 days of training, defence ministry spokeswoman Jessica Lamirande said.

The suspect's two-story red-brick home in a suburb north of Toronto was a crime scene on Tuesday, taped off and surrounded by police vehicles.

Two South Korean nationals and a Jordanian citizen were killed in the attack.