The US military routinely carries out flights over international waters, operations that it says are conducted in neutral airspace and in accordance with international law.

But Moscow has responded more aggressively to the exercises in recent months, warning in June that US drone flights over the Black Sea risked leading to a “direct” military clash.

The Russian defence ministry said it had scrambled fighter jets to intercept an “air target approaching the state border of the Russian Federation”.

“The crews of the Russian fighters identified the aerial target as a pair of US Air Force B-52H strategic bombers,” it said.

“As the Russian fighters approached, the American strategic bombers corrected their flight course, moving away and then turning away from Russia’s state border,” it said.

In June, Moscow accused the US of using its reconnaissance drone flights over neutral waters in the Black Sea to help Ukraine strike the Russian-annexed Crimean peninsula.

It said that the flights increased the risk of a “direct confrontation” between Nato and Russia, and that its army had been instructed to prepare an “operational response”.