Canada has closed its airspace to all Russian carriers in protest at the Russian invasion of Ukraine, Ottawa announced Sunday.
But the ban was quickly tested when, according to Canadian officials, a plane operated by Russian airline Aeroflot flew over the country.
Aeroflot flight 111 had departed Miami, Florida, bound for Moscow.
Announcing the measure earlier in the day, Transport Minister Omar Alghabra said: "We will hold Russia accountable for its unprovoked attacks against Ukraine."
The closure, effective immediately, aligned Canada with the vast majority of European countries.
While there had been no direct flights between Canadian and Russian airports, the decision by the world's second-largest country — Russia is the largest — promised to seriously complicate flights by Aeroflot to or from the United States, as well as to other countries to the south.
Any flight owned, chartered by or used by Russian interests — including private flights — was banned from Canadian skies, transport ministry spokeswoman Valerie Glazer told AFP in an email.
However, the Aeroflot flight "violated the prohibition", according to a tweet by government agency Transport Canada.
"We are launching a review of the conduct of Aeroflot and the independent air navigation service provider, NAVCAN, leading up to this violation," it said.
"We will not hesitate to take appropriate enforcement action and other measures to prevent future violations."
A growing list of European countries — including Germany, France, Spain, Italy, Belgium, Austria, the Netherlands and Sweden — have closed their airspace to Russian carriers in response to the invasion of Ukraine.
Britain barred Aeroflot flights on Thursday.
No flights from Russia appeared Sunday to be arriving at major US airports in Washington, Baltimore, New York, Los Angeles and Chicago.
Delta Airlines on Friday suspended a code-sharing arrangement with Aeroflot.
But the US Transportation Department has yet to announce a decision on banning Russian flights.