He says ''We're all shaken by it."
Obama says the motive for the attack remains unknown.
But he says as more becomes known, that information will be factored into U.S. security considerations.
Obama says he spoke by telephone today with Prime Minister Stephen Harper and offered him condolences on behalf of the American people.
A Canadian honour guard at the National War Memorial in Ottawa was shot and killed by a masked gunman this morning.
Gunfire also erupted inside Parliament where authorities say the gunman was killed.
Obama also expressed the American people's solidarity with Canada.
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