Nato aircraft tracked Russian strategic bombers over the Atlantic and Black Sea on Wednesday and sorties of fighters over the Baltic in what the Western alliance called an unusual burst of activity at a tense time in East-West relations.

In all, Nato said in a statement, its jets had intercepted four groups of Russian aircraft in about 24 hours since Tuesday, and some were still on manoeuvres late on Wednesday afternoon.

“These sizeable Russian flights represent an unusual level of air activity over European airspace,” the alliance said.

A spokesman stressed there had been no violation of Nato airspace – as there was last week when a Russian spy plane briefly crossed Estonia’s border. But such high numbers of sorties in one day were, he said, rare in recent years.

In the biggest exercise, four Tupolev Tu-95 strategic bombers, a Cold War icon since the 1950s and Russia’s equivalent of the US B-52, flew out over the Norwegian Sea in the early hours of Wednesday, accompanied by four refuelling tanker aircraft.