The aftershock of Thursday's London transit system attacks is reverberating through Canada's largest cities, as public transit officials stepped up vigilance and security precautions.

At least 40 people are feared dead and hundreds more injured in the attacks that struck commuters in the British capital.

In the wake of the attacks, which shut down London's massive subway and bus system, Toronto Transit Commission officials issued their own rush-hour "vigilance notice," asking both employees and passengers to be on the lookout for anything unusual. More police were also been assigned to patrol the system.

Police surveillance was also stepped up across the subway, bus and train networks that service the Montreal area, though officials cautioned there has been no specific threat.

"Following the events that happened in London this morning, we immediately increased the police presence in places of interest, for example all public transport networks,'' Montreal police spokesperson Const. Anie Lemieux said.

Canada's public safety minister, Anne McLellan, says Canada developed provisions for tighter security on transit networks after the terrorist bombings on Madrid trains last year.

She says that new system kicked in right after the London bombings.

She added that the country's major rail operators have also been alerted, and have been advised to increase vigilance.

McLellan told reporters that even though there was no specific threat against Canada, that doesn't mean the country is not at risk.

"We have never said that we are not at threat because in fact, we're one of five nations that were named by al Qaeda and therefore that is why we take these kinds of events very, very seriously."

In his own comments at a news conference in Gleneagles Thursday evening, Prime Minister Paul Martin said Canadians should be reassured by the security measures now in place.

"Canadians can feel secure that they know that all the measures that were put in place after September 11 are in place," Martin told reporters.

Transit around the globe

The heightened vigilance echoes the quick worldwide response to the morning attacks.

In the United States, the Department of Homeland Security raised its terror threat level to Code Orange for public transit systems. And in France, officials raised that country's terror alert to its second-highest level.

In Italy, security has been stepped up at airports, while Germany has increased security across the state-owned railway system and the Netherlands increased security at British buildings.

In Spain, where a series of commuter train blasts killed 191 people last March, the government has raised its terror alert to maximum.

Canada may seem far removed from the day's attacks, but if those responsible for the London blasts are indeed al Qaeda upset with Western involvement in Iraq and Afghanistan -- where Canadian forces are leading the international mission -- this country could yet be targeted.

Prime Minister Paul Martin made his concern for the safety of Canadians clear in the first statement he gave to reporters after the attacks Thursday morning.

Conveying his sympathies to the victims and their families, Martin told reporters at the G-8 summit venue in Gleneagles, Scotland, that he was immediately in touch with his top security adviser in Ottawa.

"Obviously we are monitoring the situation and we are also in touch with the British officials," the prime minister said.

At a news conference later Thursday morning, Toronto Mayor David Miller said he was actively working to ensure the city was secure.

"We have been working very hard through the city's emergency management committee ... to ensure that this city is prepared as best as possible," Miller said.

"The Toronto Transit Commission in particular has been working very hard ... to ensure that it is as prepared as possible."

'Constantly vigilant'

Watching the international response, Harlan Ulman of the U.S. Center for Strategic and International Studies said heightened vigilance may be reassuring, but it can do little to prevent an attack.

"You have millions of targets," Ulman told CTV in an interview from Washington, D.C.

"The fact is that every society and advanced country is enormously vulnerable and there's no way that we can prevent these attacks."

The only solution, he said, would be to address the root causes of the assaults, rather than trying to root out perpetrators after the fact.

"It seem to me we're going after symptoms, going after terrorists one at a time believing that the problem is terror and not the political problems and pressures that really cause these people to use violence and terror to achieve their ends."

In the meantime, security expert David Harris said the current global political climate demands governments remain constantly vigilant.

"Really, the honest truth is that we should be running ourselves as though this was the day-to-day threat that we're all facing because it's been so defined by our enemies from bin Laden on down," the former CSIS chief of strategic planning told CTV's Canada AM.

At his evening news conference Thursday, Martin said Canada could be a terror target, but sought to assure Canadians not to panic.

"We know very well that all countries are targets, and what's happened in London could happen anywhere else," Martin said in French. Even though there is no present threat against Canada, the prime minister inisted, "we have to be vigilant."

McLellan said that there have not been any reports of Canadians among the victims of the London blasts.

"To the best of our knowledge, we are not aware of any Canadian casualties at this time," McLellan told reporters in Edmonton, Alberta.

"We know there are several Canadians of note in England, most notably Premier Dalton McGuinty of Ontario. He has been located and is fine and not affected by any of these bombings," Liberal MP Dan McTeague said.

According to the foreign affairs parliamentary secretary, federal Justice Minister Irwin Cotler and Chief Supreme Court Justice Beverley McLachlin -- both of whom are also in England -- have been accounted for.

"They are OK as well,'' McTeague said.

Those trying to get information about Canadian friends or relatives in Britain are asked to contact the Department of Foreign Affairs hotline with a full name, birthdate, and passport number.

The toll-free phone number is: 1-800-606-5499.