The campaign to be the next mayor of Toronto was dominated by issues of safety and security on a day when a soldier was gunned down in Ottawa and gunfire was exchanged in the House of Commons, with Doug Ford declaring he would "round up" all the people on the RCMP's watch list if he had his way.

The three leading candidates – John Tory, Olivia Chow and Mr. Ford – expressed their sympathies to the family of the fallen soldier, breaking format at the beginning of a debate Wednesday night to offer their comments on the tragedy in place of the planned opening statements.

But the most controversial statements came after live cameras were turned off and Mr. Ford spoke with reporters. Asked how he would handle the current situation, he outlined his preferred action.

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"I understand there are over 90 people on this watch list that the RCMP have been watching," he said. "If you're asking me, I'd be rounding up all 90 of them and finding out, because they came from the same cell. This is unacceptable. We can't tolerate it in this city. I wouldn't tolerate it and I'd make sure we rounded up every one of these characters."

Asked about due process, Mr. Ford said he would not "throw them in jail," just question them.

"You have to take a hard line. You can't sit down and be soft with these people. … We don't want people like this in our country, in our city," he said.

Mr. Tory and Ms. Chow said such matters should be left in the hands of law-enforcement agencies.

Ms. Chow said the details aren't known yet, and the experts need to be respected to do their job. "Let us not second-guess them. This is not the time to do so."

Mr. Tory agreed. "We have all kinds of people who are experts and who devote themselves to keep us safe. I would like to leave the decision of how to deal with those people to them," he said.

During the debate, the issue of security at city hall was raised by Mr. Ford who said it is time to install metal detectors and beef up protective measures at the building that houses the country's sixth-largest government.

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Both Ms. Chow and Mr. Tory said such issues should be left to law enforcement agencies and should only happen after all the facts about Wednesday's events are known and the public has been consulted.

As events in Ottawa continued to develop, city hall responded by restricting access at some doors and erecting metal fencing outside the main doors. While the public continued to come and go freely through the front doors, by the afternoon police officers stood by in the square and security guards stood by other doors.

Deputy Mayor Norm Kelly said he had asked that the flag at city hall be flown at half-mast.

"What a few horrible days," Mr. Kelly said Wednesday, leaving his own re-election campaign to address a hastily called news conference at city hall.

"I want to ensure Torontonians that there is no immediate threat to our city, its people or its institutions," he said, but he asked citizens to report any unusual activity and said the city government had moved to an "enhanced level of security" at City Hall, Metro Hall, civic centres and Union Station.

With a report from Marcus Gee.