US President Barack Obama has condemned fatal shootings in Canada as "outrageous attacks".
"We're all shaken by it," he said.
Obama says the motive for the shootings remains unknown, but that as more becomes known, that information will be factored into US security considerations.
"We have to remain vigilant," he said.
Obama spoke by telephone with Canadian Prime Minister Stephen Harper.
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The US president said he offered condolences on behalf of the American people.
A Canadian soldier standing guard at a war memorial in the capital of Ottawa, Ontario, was shot and killed on Wednesday.
Gunfire also erupted inside parliament nearby, and authorities say at least one gunman was killed.
On Monday, authorities said a recent convert to Islam killed one Canadian soldier before being shot dead by police.
Obama spoke after holding a meeting with members of his Ebola response team in the Oval Office.
The Department of Homeland Security says there is no specific threat to the US related to the Canada shooting incident.
