European defense officials have been worried about an increasing number of Russian bombers entering Western airspace.
A pair of Tupolev Tu-160 Blackjack bombers -- the largest jet-powered combat aircraft ever built, capable of carrying nuclear missiles -- last month entered British airspace over Northern Scotland, Deutsche Welle reports.
Two Tornado fighter jets from the British air force intercepted the supersonic bombers, accompanying them for four hours until they left British airspace.
Similar incidents have occurred in recent years; London has said Russian planes have penetrated British airspace more than 20 times since the start of 2009.
Stefan Meister, a Russia expert with the German Council on Foreign Relations, said that some penetrations might be accidental. He didn't rule out that there a Kremlin-authored strategy might be behind them.
"The infiltration into the airspace is one of the ways the Russians try to prove that Russia is still a power that should be treated with the respect," Meister told United Press International in a telephone interview.
A friend of military muscle-flexing, Russian Prime Minister Vladimir Putin in 2007 reactivated long-range patrols by nuclear-capable bombers after they hadn't been sent out over the world's oceans for 15 years.
The move came as the Kremlin expanded its grasp into the Arctic, as one of its submarines planted a flag in the seabed in territory it considers its own at the North Pole in 2007.
The Arctic is being transformed by climate change.
Melting ice sheets will leave the oceans in the region possibly ice-free during the summer months. This is opening a new Atlantic-Pacific shipping channel and makes the vast oil and gas resources lying under the seabed more accessible.
Patrol flights over Arctic waters have increased and Russia has given no sign that this will change – much the contrary.
Putin this year announced he wants to beef up the Russian air force.
The Kremlin in February unveiled its fifth-generation fighter jet and Putin wants his country's military industry to start working on a new strategic bomber.
A launch of a new bomber program would be a giant project for the Russian aviation industry, which has been helped by numerous orders and major financial aid packages over the past years. Yet it's only one step of many that will see a major overhaul of the Russian air fleet.
Moscow plans to commission 1,500 new planes and helicopters to modernize the air force by 80 percent, the government said.
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