This story was updated at 1:50 p.m. to include comments from Ottawa Tourism and risk consultant Chris Mathers.
Canada's capital will do everything it can to prevent an attack when it hosts the country's 150th birthday next month but no amount of preparation can guarantee 100 per cent safety, Ottawa's mayor says.
"When you see a tragedy that took place in London and on London Bridge and in Manchester, you think could that happen here and sadly, the answer is yes," Mayor Jim Watson said Sunday, the day after the latest attack in Britain, on London Bridge, that left seven dead and scores injured.
Prime Minister Justin Trudeau said a Canadian was one of those killed. Family members identified her as Christine Archibald, originally from British Columbia.
With Ottawa preparing to host one of the largest Canada Day celebrations, Watson said there will be an extra security measures and a noticeable police presence on July 1, but that's no guarantee.
"There's no 100 per cent solution to terrorism." Watson said after taking part in a tree-planting ceremony at Ottawa City Hall.
"It's always a wake-up call for us in roles of leadership that we have to vigilant in the world we live in. A simple knife and a motor vehicle can be the new weapon of choice for a terrorist or for someone who wants to cause harm to people in a community."
Watson described the extra precautions Ottawa took for its most recent outdoor New Year's Eve celebrations in response to December's truck attack on a Berlin Christmas market. A truck driven by a man who claimed affiliation with the Islamic State group rammed the market killing 12 people and leaving dozens dead.
Ottawa placed front-end loaders and dump trucks at key cross streets to protect a long human chain of hundreds of school children carrying torches to mark the start of 2017 and the Canada 150 festivities, said Watson.
He said trucks were specifically brought in to ensure those children "were not going to be harmed or run over."
Watson said similar precautions will be taken for the upcoming Canada Day celebration, which usually sees hundreds of thousands filling Ottawa's streets each July 1, but will likely be larger this year.
Intelligence gathering in advance of the Canada 150 celebrations and extreme vigilance during the Parliament Hill events will be key, said Chris Mathers, a former RCMP officer who now works as a crime and risk consultant.
"There will be people scanning the crowd," Mathers said. "There will be tactical teams, there will be bomb-disposal teams. From now on at any large gathering, that's what you're going to have. It's just inevitable. The costs are astronomical."
Police and security officials "know who the bad guys are" and will be watching them closely, Mathers said, adding it is difficult to know when a lone-wolf attacker might act.
"You decide you're going to drive a vehicle into a bunch of people and then get out and start stabbing a bunch of people, how do the security services find out about that? If you don't say anything to anyone, you just get it in your head to do it, it's very difficult to stop."
Jantine Van Kregten, Ottawa Tourism's director of communications, said she's seen no evidence that people are changing plans to be in Ottawa for Canada Day, given the recent terrorist activity overseas.
Security is always top of mind for special events in Ottawa, and Canada Day is one of the biggest of them all, Van Kregten said.
"That is the biggest day of the year so it is not something they're just addressing now because of recent attacks in London," she said in an interview.
"It is a reality of our lives today that in our communities we need to be vigilant. That is definitely the case here in Ottawa."
Liberal MP David McGuinty, who is to chair a new, top-level national security committee, said the federal government is consulting with communities across Canada on their Canada Day security requirements.
Municipal leaders across Canada observed a moment of silence Sunday in honour of those killed in London at the closing session of a meeting of the Federation of Canadian Municipalities in Ottawa.
The organization's outgoing president Clark Somerville told the gathering in his final speech that for "every deranged individual" who takes a life, there are many more who represent the best of humanity.
"This is what our cities and communities are made of. We're strong, resilient and unbreakable."