The UK has summoned the Russian Ambassador to the Foreign Office to explain why the country's long-range bombers had flown over the English Channel in the latest incursion into British airspace.

The Russian Bears were picked up by radar off the coast of Bournemouth, forcing the Civil Aviation Authority to reroute passenger jets and shadowed by two RAF Typhoons.

It follows a similar incident in November in which Typhoons from RAF Lossiemouth were sent to shadow Soviet-era Tupolev Tu-95 aircraft spotted over Scotland. There had been an earlier incident involving two Russian Bears over the North Sea.

A government source said it was being viewed as "a significant escalation" and marked a change in strategy since Russian aircraft had previously largely confined themselves to flying close to Scotland.

"It was very dangerous. civil aircraft flying to the UK had to be rerouted," the source said. "The Russians were flying with their transponders turned off so could only be seen on military radar. They haven't flown this far south before."

Russian Ambassador Alexander Yakovenko will now have to account for the incident. The Foreign Office said the episode was part of an increasing pattern of "out of area operations" by Russian aircraft.

"The Russian planes caused disruption to civil aviation. That is why we summoned the Russian Ambassador today to account for the incident," a spokesman said.

Last year, Nato forces conducted more than 100 interceptions of Russian aircraft, about three times as many as in 2013, amid increased tensions between the West and Moscow over the Ukraine crisis.

British Foreign Secretary Philip Hammond said in December he was concerned by "the extremely aggressive" probing of Britain's airspace by Russian military aircraft after a spate of interceptions off the Scottish coast.

Hammond, a former defence minister, had previously said the sharp increase in such activity in recent years was because of a Kremlin military overhaul that had been overlooked by many.