OTTAWA — Two people are dead after at least one gunman stormed Parliament Hill on Wednesday morning.

One of the dead is a soldier, Cpl. Nathan Cirillo, 24, a reservist with Argylls of Canada - 91st Canadian Highlanders in Hamilton, Ont., who was standing guard at the National War Memorial. The other is the gunman, Michael Zehaf-Bibeau, born in 1982, who opened fire in Centre Block across the street.

Two U.S. officials said that U.S. agencies have been advised that Zehaf-Bibeau was a Canadian convert to Islam. One of the officials said that the man was from Quebec.

Police continued to search vehicles in downtown Ottawa, where blocks of the city's core were locked down all day.

Gunfire exploded shortly before 10 a.m., just outside where the Conservative caucus was meeting.

The shooter was met with return fire — dozens of shots were heard — and was killed outside the parliamentary library.

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During the exchange of gunfire through the main Hall of Honour, one parliamentary guard was shot in the leg, another was grazed by a bullet and a third person suffered minor injuries. They were taken to Ottawa Hospital where they were treated and released.

Sergeant-at-arms Kevin Vickers is being widely praised as a hero after he stopped and killed the shooter just outside the Parliamentary library before he managed to reach the MPs.

"All the details are not in, but the sergeant-at-arms, a former Mountie, is the one that engaged the gunman, or one of them at least, and stopped this," Veterans Affairs Minister Julian Fantino said from inside Parliament. "He did a great job and, from what I know, shot the gunman and he is now deceased."

In the days leading up to the shooting, Canada’s terrorist threat level had been elevated for the first time in four years.

“I think it’s still too early to confirm, but from our reaction, (the attack) caught us by surprise,” RCMP assistant commissioner Gilles Michaud said.

“If we would have known that this was coming, we would have been able to disrupt it... The threat level on Parliament Hill, we’ve been operating at the medium level for the past number of years, and that’s the level we’re operating at now.”

The Prime Minister's Office said Stephen Harper was safely removed from the building.

"(Harper) was addressing caucus, then a huge boom, followed by rat-a-tat shots. We all scattered. It was clearly right outside our caucus door," Treasury Board President Tony Clement said.

At the time of the shooting the Opposition New Democrats were holding their own weekly caucus meeting in Parliament. A tweeted picture sent from the room showed a pile of chairs jammed up against the main door to prevent anyone from entering.

NDP Party members put chairs against the doors when shooting starts in their hallway during attack on Parliament. pic.twitter.com/JYg3fdM00a — Robert Yuna (@ryuna4) October 22, 2014

A construction worker who was on the scene in Ottawa when the shooting began told Reuters he heard a gunshot, and then saw a man with a scarf over his face running towards Parliament.

"He was wearing blue pants and a black jacket and he had a double-barrelled shotgun and he ran up the side of this building here and hijacked a car at gunpoint," Scott Walsh said.

The driver got out safely, then the man drove the car to the Centre Block on Parliament Hill, where construction work is underway, Walsh said.

The suspected gunman rushed past a woman with a child in a stroller, who ran away screaming. He didn't attack the woman or child, Walsh said.

The suspect car remained parked on Wellington St., roughly between the War Memorial and Parliament Hill; its licence plates had been removed.

Canada announced this month it was joining the battle against Islamic State fighters who have taken over parts of Iraq and Syria.

Wednesday's attacks took place as the federal government prepared to boost the powers of the Canadian Security Intelligence Service, to allow the spy agency to track and investigate potential terrorists when they travel abroad and ultimately prosecute them.

RCMP assistant commissioner Gilles Michaud said Canada's security alert level was recently raised, but the security level on Parliament Hill was kept at "medium."

The shooting comes just two days after a newly converted jihadist ran down two soldiers with his car in a parking lot south of Montreal, killing one.

— with files from Joe Warmington, Aeden Helmer, Jessica Hume, Reuters

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