Photo: The Canadian Press

Thousands of fentanyl-laced pills described by police as "potential doses of death" and nearly two dozen guns were seized this week as officers arrested 18 people in an international investigation into organized crime, Ontario Provincial Police said Thursday.

Hundreds of officers fanned out through parts of Ontario and Quebec as part of calculated, simultaneous raids on 22 locations on Wednesday, seizing pills containing the deadly opioid fentanyl and 23 firearms, OPP Deputy Commissioner Rick Barnum told a news conference.

"By dismantling a criminal operation of this magnitude, we've literally prevented more than 11,000 doses of death of fentanyl and illegal guns from killing people in our communities," Barnum said.

The investigation began by targeting multiple criminal groups trafficking firearms and drugs along the Highway 401 corridor between the Greater Toronto Area and Montreal, he said.

Investigators then found that drugs were also being smuggled from Canada into the United States, and Drug Enforcement Agency officials in Connecticut became involved in the operation, Barnum said.

The 18-month investigation — known as Project Silkstone — also involved the RCMP, Quebec provincial police, Montreal police and the Canada Border Services Agency.

Over the course of the probe, OPP say investigators seized 11,500 pills containing fentanyl, eight kilograms of cocaine and 7.5 kilograms of ecstasy, among other drugs and drug equipment.

Barnum said the fentanyl products were being produced in Montreal and moved into Ontario. He said that was further proof fentanyl is not only being sold as an opioid, but also as a cutting agent — mostly for economic reasons.

"We have audio recordings of drug traffickers who callously admitted that the enormous profits that can be made from fentanyl far outweighs the potential overdose deaths that can come about as a result of them dealing these drugs," Barnum said.