A gunman fired on sunbathers at a beach near two hotels in the coastal resort city of Sousse. The department says 826 Canadians were known to be in Tunisia.
However, that number is only an estimate, since registration is voluntary and the figure is typically not fully representative of the actual number residing or visiting an area.
The attack came the same day a suicide bomber killed worshippers at a Shiite mosque in Kuwait and a man with links to Islamic radicals rammed a vehicle into a gas factory in southeastern France.
Two people were injured in an explosion at the factory and the severed head of the suspected attacker's employer was left hanging at the entrance.
Prime Minister Stephen Harper said he was "saddened and angered" to learn of the attacks.
"On behalf of all Canadians, Laureen and I offer our deepest condolences to the family and friends of those lost today and a speedy recovery to those injured," Harper said in a statement.
Canadian agencies have offered French authorities Canada's full support, he added.
"We mourn today with France and stand behind our close friend on this dark day," the statement said.
"Canada also strongly condemns the unfolding terrorist attacks in Kuwait and Tunisia that have killed and injured many. Our hearts and prayers are with the families and friends of all victims."
Speaking in Montreal, NDP Leader Tom Mulcair urged Canadians to show the same support to the countries targeted Friday that the world showed Canada in the wake of the attack on Parliament Hill on Oct. 22.
"We've got to show the same strong support for the countries like France and Tunisia that have been the objects of today's attacks," Mulcair said.
"We've got to be strong and determined in our efforts to deal with terrorism. We should never back away from that fight. We have to be strong and present on the world stage."
Foreign Affairs says Canadian citizens in Sousse, Tunisia, requiring emergency consular assistance should contact the Embassy of Canada in Tunis at 216-70-010-200, or call the department's 24/7 Emergency Watch and Response Centre collect at 613-996-8885. An email can also be sent to email@example.com.
Friends and relatives of Canadian citizens known to be in Sousse should contact Foreign Affairs' 24/7 Emergency Watch and Response Centre by calling 613-996-8885 or 1-800-387-3124, or by sending an email to firstname.lastname@example.org.
— With files from the Associated Press
Follow @JimBronskill on TwitterSuggest a correction