U.S. President Barack Obama was briefed on the shootings by his top homeland security adviser. White House press secretary Josh Earnest said American officials were in touch with their Canadian counterparts and had offered assistance, and Obama and Prime Minister Stephen Harper spoke by phone early in the afternoon.
"The thoughts and prayers of everybody here at the White House go out to the families of those who were affected by today's shooting in Canada as well as to the family of the soldier who was killed earlier this week," Earnest said, referring to the hit-and-run attack in St-Jean-sur-Richelieu, Que., that killed Warrant Officer Patrice Vincent.
"Canada is one of the closest friends and allies of the United States and from issues ranging from the strength of our NATO alliance to the Ebola response to dealing with ISIL, there is a strong partnership and friendship and alliance between the United States and Canada," said Earnest. "The United States strongly values that relationship and that relationship makes the citizens of this country safer."
Earnest said he was not aware of the threat level being raised in the United States as a result of what happened in Ottawa or any added security measures at the White House or on Capitol Hill.
State Department spokeswoman Marie Harf told reporters that Secretary of State John Kerry was also briefed on the shooting and is monitoring the situation closely. The U.S. Embassy in Ottawa was put on lockdown, she said.
United Nations Secretary General Ban Ki-moon also said his thoughts were with Canadians.
"The secretary general is aware of the situation unfolding in Ottawa, including in the Canadian Parliament, during which a soldier has reportedly been shot. He hopes the situation will be brought quickly under control by Canadian law enforcement authorities. His thoughts are with the people and government of Canada at this difficult time," a statement provided to CBC News read.
British Prime Minister David Cameron was another world leader who offered his support to Canada. "I'm appalled by today's attack in Ottawa," he wrote on Twitter, adding that he is offering his full support to Harper "and the Canadian people as they deal with this incident."
British Foreign Minister Philip Hammond said on Twitter he was "horrified" to learn of the shootings.
"Our thoughts are with you," he wrote in response to a tweet from his counterpart, Canada's Foreign Affairs Minister John Baird.