The military increased security Wednesday at the Tomb of the Unknowns at Arlington National Cemetery after fatal shootings at a Canadian war memorial and Parliament, even though the FBI and the Homeland Security Department said there was no specific threat against the U.S.

President Barack Obama condemned the shootings in Canada as "outrageous acts."

"Obviously the situation there is tragic," Obama said, adding, "we're all shaken by it." He confirmed the death of a Canadian soldier, and extended his condolences.

The Canadian soldier had been standing guard at the National War Memorial in the capital of Ottawa, Ontario. Gunfire also erupted inside Parliament, and authorities in Canada said at least one gunman was killed.

The White House said Obama spoke by telephone with Canadian Prime Minister Stephen Harper. The U.S. has offered to help the U.S. ally with its response, and Obama expressed the American people's solidarity with Canada.

In a statement, the FBI said it had reminded field offices and government partners to remain vigilant in light of recent calls for attacks against government personnel by what it described as terrorist groups and like-minded individuals. "We stand ready to assist our Canadian partners as they deal with the ongoing situation in their capital," it said.

The agency and Homeland Security said there was no specific threat against this country.

A U.S. Capitol police spokesman said the force remained at a post-9/11 "heightened level of awareness," but did not make any significant modifications as a result of the shootings in Canada.

"The USCP continues to monitor and track the Canadian event," Officer Shennell Antrobus said.

Authorities increased security at the Tomb of the Unknowns, which draws 4 million tourists a year. The Military District of Washington, which oversees the 3rd U.S. Infantry Regiment, known as The Old Guard, that protects the tomb, said the added security was a "precautionary measure."

The U.S. Embassy in Ottawa was also placed on lockdown as a precaution.

It was unclear whether Wednesday's shootings were terrorism-related.

Earlier this week one Canadian soldier was killed and another injured in a hit-and-run crash. Authorities have said the suspect in that earlier case was a recent convert to Islam who is suspected of having jihadist ambitions. The suspect was shot to death by police after the deadly crash.

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Associated Press writers Matthew Barakat in McLean, Virginia, Rob Gillies in Toronto, Jeremy Hainsworth in Ottawa, Ontario, and Matthew Daly in Washington contributed to this report.