TORONTO - Police and intelligence agencies are concerned that the kind of Black Bloc tactics employed by a mob of militant protesters at the G20 is on the rise.

And CSIS says authorities weren't expecting the intensity of the violent outbursts in Toronto.

"Are we aware of these type of tactics? I think everyone is," Marc Boyer, of the Canadian Security Intelligence Service, said Sunday.

"Anyone who has been following these things over the years has seen more and more of this type of activity. I don't think anyone was expecting it to that degree."

The so-called Black Bloc strategy was deployed Saturday by a small splinter group that infiltrated what had been a large, peaceful protest in Toronto's downtown.

Roving militants emerged from the crowd to destroy symbols of capitalism, then melted back into the larger group and shed their disguises — black hooded sweatshirts, pants and masks.

The result was the most violent outburst the city has ever seen.

Police stood by Saturday as the anarchists set their cruisers ablaze. But by Sunday their attitude had changed, and almost anyone on the streets wearing black was stopped and searched.

Toronto police had been expecting these kinds of tactics to tarnish summit protests, and had been investigating Black Bloc activities for months in an effort to keep them to a minimum as the world's eyes turned to the city.

During a special bail hearing at an Ontario court for people charged with G20-related offences, Crown prosecutor Vincent Paris described a large-scale police investigation into the activities of Black Bloc that began in April 2009.

Investigators had been targeting at least 15 people, according to court documents.

Many of the people on that list have already appeared in court.

Jaggi Singh, one of Canada's most high profile social justice activists and anarchists, was one of the police targets.

He leads the Montreal sect of No One Is Illegal, which reports that at least two of its members have been arrested.

"King & Bay is the heart of Canadian colonial capitalism, which projects its misery all over the world," Singh posted on Twitter on Saturday, after militant protesters set a police car on fire at the intersection.

Four others on that list — Amanda Hiscocks, Leah Henderson, Alex Hundert and Peter Hopperton — have been arrested and are alleged members of the Southern Ontario Anarchist Resistance, a group that advocated "militant and confrontational" action at the G20 in a memo circulated online.

The group called for its members to join Saturday's People First march, "before continuing on towards the fence to confront the police state and Toronto's corporate culture."

"This action will be militant and confrontational, seeking to humiliate the security apparatus and make Toronto's elites regret letting the dang G20 in here," it said.

Plans for Sunday were less organized. The group called for "autonomous direct action" all day, which it described as "diverse and creative actions aimed to disrupt business-as-usual."

The group encouraged members to form what it called "affinity groups," small groups of people, "about 3-10 or so, who are interested in similar tactics and have similar levels of comfort."

Banding together in smaller groups within a larger crowd is a popular Black Bloc organizational tactic.

Black Bloc tactics were also employed by violent protesters at the Vancouver Olympics, but on a much smaller scale, Boyer said. There, a small group of protesters in black smashed the window of Olympic sponsor, Hudson's Bay Co.

Toronto police have formed a G20 Investigative Unit in part to find the elusive Black Bloc protesters, whose faces are rarely seen.

They are calling on the hundreds of people who took pictures at the protests to send in their photos to help identify the perpetrators of Saturday's violence.

Police brass and the mayor have defended Saturday's police response, saying they accomplished their first priority — keeping protesters away from the summit security zone.

But Judy Rebick, a social justice professor at York University, is questioning the police response to the riots. She believes police allowed crowds to get out of control, despite having informants in the crowd.

"What they could have done is arrest the Black Bloc at the beginning before they had a chance to be part of the bigger crowd and that's what they didn't do," she said.

It's likely police were able to target certain individuals and groups, and even some of their plans, he said.

Still, "having surveillance on all of those guys is kind of like, impossible," Juneau-Katsuya added. "Too many people, too many targets."

The militant demonstrators are extremely agile and mobile, making it extremely difficult to keep tabs on them and their guerilla tactics.

"They can run and they can split themselves also in several cells. They change costume along the way as well," he said.

"They employ the defence that being in the general crowd offers and the general opinion would totally turn against the police if they were to charge indiscriminately in the crowd."

Const. Rodney Petroski of the G20 security unit said police have been looking for background information on anarchist groups that focus on unlawful tactics, but refused to elaborate.