A little known anti-military radical group has claimed responsibility for the bombing that ripped through a Canadian Forces recruitment office in Trois-Rivieres, Que., early Friday.

The blast occurred at 3 a.m. when the building was empty. The extent of the damage has not yet been assessed, but the building’s windows and door were shattered.

Police received a bomb-threat call 20 minutes before the explosion, and no one was injured in the attack, which the Canadian Forces said it considers a “single and isolated incident.”

A group calling itself Resistance internationaliste — claiming to have carried out two other bombings in the province — issued a statement Friday alleging it detonated an explosive in the centre. In a two-page email, the group lashed out at Canada’s military practices and ideals, the war in Afghanistan and police “violence” at last weekend’s G20 summit in Toronto.

“This operation against the recruitment centre is our resistance to the army brainwashing and eye-catching soliciting of young people confronted with the vacuum of a demeaning society,” the group wrote.

Quebec provincial police Sgt. Eloise Cossette confirmed a group has come forward to claim responsibility for the explosion.

“We are investigating one particular organization, but at this point, we are not ruling out any other possible suspects,” she said.

David Harris, a former chief planner for the Canadian Security Intelligence Service, said incidents such as these should be taken seriously, noting they tend to become more common as fringe elements take to the streets to show their discontent.

“This is a concern because there seems to be some developing trends of illegal violent activity that mascarades under a political mantle,” said Mr. Harris, now a lawyer involved in criminal and national security matters. “Unfortunately, I suspect we are going to have considerably more of this kind of thing as we find radicalism propagating itself.”

Mr. Harris said he has no knowledge of the Resistance internationaliste, but added: “One has to ask, if we aren’t dealing with levels of alienation that say something somewhat profound about our society . . . why do people feel that they would be justified in making war against their own society?” he said.

The group — previously known as the Initiative de resistance internationaliste — has already made its presence known in Quebec.

It claimed responsibility in 2006 for bombing the car of a spokesman for Canada’s petroleum industry and, in 2004, for a failed attempt to topple a Hydro-Quebec transmission tower carrying electricity to the United States.

The group made a brief reference to the Queen’s visit to Canada.

“As to the soldiers of the Canadian army, let us be clear, they are in no way ‘ours,’ they belong to the person to whom they foolishly pledge allegiance, her Majesty Elizabeth II,” the email read.

Opposition to the war in Afghanistan is higher in Quebec than in any other province, at nearly 75%.

Provincial police are leading the investigation into the centre’s bombing, with the help of the RCMP.

A team of bomb specialists with sniffing dogs has been dispatched to the scene.

Following the attack, the Defence Department increased security measures at its other facilities in the province, including sweeping for suspicious packages in public areas and boosting inspections at offices.

“We have no information at this time to make us believe that such an incident may happen at other Canadian Forces installations, but we remain vigilant,” said Defence Department spokesman Andrew McKelvey.