Canadian fighter jets were scrambled twice in the past two weeks to track Russian bombers over the Arctic, patrols near North American airspace that government sources say have increased in 2014 compared with the previous two years.

The Canadian government believes at least some of these patrols, in particular similar Russian flights off the U.S. West Coast, are "strategic messaging from Moscow" in response to tensions between the West and Vladimir Putin over Ukraine, sources say.

Defence Minister Rob Nicholson offered few details about the new incidents after revealing them in the Commons on Thursday. However, he said the flights demonstrate "the need for ongoing vigilance" in Canada's north. "We continue to see Russian military activity in the Arctic. The Canadian Armed Forces remain ready and able to respond."

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Government sources familiar with the matter said that, in both recent cases, the bombers entered Canada's Air Defence Identification Zone in the Arctic, a band of airspace north of the country's main land mass.

In one instance, the Russians turned back when Canadian fighters reached them, the sources said, and in the other, Moscow's aircraft had veered away before the CF-18s arrived.

The Putin government has previously accused Ottawa of overreacting to Moscow's training flights and making hay out of the "Russian bear in the air" for political reasons.

Speaking about the flights, a spokesman at the Russian embassy in Ottawa said Canada and Moscow usually have a working military relationship to address any "misunderstandings in this regard" – open lines between the two countries' "chiefs of staff of the armed forces."

Unfortunately, said Andrey Grebenshchikov, second secretary at the embassy's political section, this communication channel is no longer open as a result of strained relations over Crimea.

"Regretfully, due to the crisis in Ukraine, the Canadian government has recently frozen all contacts at this level," Mr. Grebenshchikov said. He also repeated Moscow's standing comment that it has no interest in militarizing the Arctic.

Cold-War-era training flights by Russian aircraft were suspended when the Soviet Union fell. In 2007, flush with money from high oil prices, the Russians resumed these air exercises – prompting monitoring by North American Aerospace Defence Command (NORAD) in response.

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The concern Ottawa voiced about the flights on Thursday is a shift of tone. As recently as March, Prime Minister Stephen Harper publicly played down any risk that conflict between the West and Russia over Ukraine could spill over into the Arctic.

But government sources said on Thursday it is clear that patrols are on the increase, and at least some appear to be a tit-for-tat response to the West's censure of Moscow over Ukraine. Led by the United States, Western leaders slapped sanctions and heaped condemnation on Russia for its seizure of Ukraine's Black Sea peninsula of Crimea earlier this year.

Last week, NORAD reported an episode in early June where two Russian long-range bombers were spotted just 80 kilometres off the California coast, prompting the deployment of U.S. warplanes to track their flight.

More possible conflict is on the horizon between Canada and Russia.

Moscow's departing ambassador told The Canadian Press on Thursday that Russia would consider it provocative if Ottawa joined the U.S. ballistic missile defence shield as a Senate report urged this week.

Ambassador Georgiy Mamedov said signing up for the program would aggravate relations further.

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He also said participating in the defence shield would be a waste of Canada's money.

"We will consider it to be a politically provocative, though it won't change any balance, it won't be necessary for your security or American security. They don't need you," Mr. Mamedov said.