ISIS sympathizer Aaron Driver, who died during a confrontation with police in Strathroy, Ont., yesterday, had made a martyrdom video stating his intention to carry out an attack at a "highly populated" area, but did not name a specific location, police said.

The video prompted the RCMP to warn officials at Toronto's Pearson airport, Metrolinx and the TTC at about 11:30 a.m. ET Wednesday, hours before Driver was killed as he sat in the back of a cab in Strathroy, located 30 kilometres west of London, Ont.

At a news conference Thursday, RCMP Deputy Commissioner Mike Cabana said police, acting on a tip from the FBI, were alerted to an imminent threat made by Driver in a martyrdom video. On the video, a masked Driver praised ISIS attacks in Europe and vowed revenge for allied attacks against ISIS. He railed against western "enemies of Islam" and warned that the only solution would be the "spilling of your blood."

Cabana said the threat alluded to an attack at an urban centre during either the morning or afternoon hour, but that no specific city was named. Police aren't certain how far Driver intended to travel to carry out his planned attack when he died. Police confronted Driver in a taxi cab in Strathroy when he detonated an explosive device, injuring himself and the driver. It's not yet known whether he was killed by the explosive or police gunfire.

Police said if Driver had been able to leave Strathroy before police arrived, the ending could have been much different.

"This could have ended with greater loss of life," said Cabana.

The tip came to the RCMP at 8:30 a.m. By 11:30 a.m., police were fairly certain Driver was the person who made the video. At about the same time, a warning went out to police agencies across Ontario and to airport and transit officials in Toronto.

Brad Ross, spokesman for the Toronto Transit Commission, told CBC News the TTC was made aware of a terror threat investigation at around noon ET Wednesday.

"We were given no specific information on the location or targets, but we were advised that this was an ongoing investigation of a credible threat," Ross told CBC News.

As a precaution, Ross said, the TTC issued a "see something, say something" vigilance notice to all staff.

Officials with the Greater Toronto Airports Authority, which operates Pearson International Airport, also confirmed to CBC that they received a warning from authorities Wednesday about a non-specific threat. As a result of that warning, the GTAA worked to enhance security.

GTAA: we were made aware of a non-specific threat yesterday. —@CBCKatie GTAA: As a result of this, we worked with partners responsible for airport security to enhance our security posture. —@CBCKatie

Metrolinx operates GO Transit, the regional transit system that connects Toronto to its suburbs and carries about 250,000 passengers daily, the bulk of them travelling to and from Union Station.

Metrolinx spokeswoman Anne Marie Aikins said the agency also raised its level of vigilance Wednesday, and worked closely with national, provincial and local forces in response.

Toronto police spokesman Mark Pugash said Thursday morning that there is, "nothing at this point to indicate Toronto was targeted," and added that it's an RCMP matter.

'Potential' threat after device detonated

Police told Driver's family he was killed because he had another device and planned to detonate it. A senior police official told The Canadian Press on Wednesday that the man allegedly planned to use a bomb to carry out a suicide mission in a public area.

Driver agreed to the conditions of a peace bond when he appeared in a Winnipeg court earlier this year after his arrest in June 2015 for participating in a terrorist group. He moved to Strathroy in July 2015.

But although he was on the police radar, Cabana said Driver was not under constant surveillance.

"​Our ability to monitor people 24 hours a day, seven days a week doesn't exist," said Cabana. "We can't do that."