Military-style security was arrayed outside a courthouse near Toronto on Saturday as 17 terrorist suspects were brought to face charges they planned to detonate three tons of explosives in and around Canada's largest city of Toronto.

Royal Canadian Mounted Police (RCMP) assistant commissioner Mike McDonell, right, speaks as Canadian Security Intelligence Service (CSIS) assistant director of operations Luc Portelance looks on in Toronto

Assistant Commissioner Mike McDonell, head of criminal intelligence and national securtity for Canada's Royal Canadian Mounted Police, said the arrests were made when it became clear the men were about to strike.

At a press conference in Toronto on Saturday, McDonell showed samples of the evidence gathered against the men including the main explosive fuel - ammonium nitrate - a common fertilizer. McDonell said the group ordered and received three tons of the chemical for use in terrorist attacks. "If I can put this in context for you, the 1995 bombing of the Murrah Federal Building in Oklhoma City that killed 168 people was completed with only one ton of ammonium nitrate," he said.

Canada is not immune to terrorism, Mr. McDonell warned. While this bombing plot was foiled, the investigation into this and other terrorist threats remains on-going, he said.

At the same press conference, Toronto Police Chief Bill Blair noted his officers are investigating threats against his city's transit system.

The 12 men and five young offenders arrested and charged in the Friday night police raids range in age from 19 to 43 years old. Most are Canadian citizens and live in and around Toronto.

Mr. McDonell described the group as inspired by al-Qaida, but said so far investigators found no link between them and Osama bin-Laden's terrorist network.

Luc Portelance, Assistant Director of Operations for CSIS- the Canadian Security and Intelligence Service - said the threat of ideologies preaching violence and murder is a global one. "Any movement that has the ability to turn people against their fellow citizens is obviously something CSIS concerned about," he said.

While this plot had been foiled, Mr. McDonell made it clear Canadians police and security forces remain very concerned about what they don't know. And what they fear was visible at the courthouse where steel barriers and three police checkpoints armed by officers with M-16 assault rifles and submachine guns separated the public from the entrance.