MOSCOW (Reuters) -Russia scrambled two Sukhoi Su-30 fighter jets to escort a pair of U.S. B-1B strategic bombers over the Black Sea, Russia’s defence ministry said on Wednesday, an incident that coincided with a visit to the region by the U.S. secretary of defense.

The supersonic U.S. Cold war-era planes were originally designed to carry nuclear bombs and missiles but now carry conventional payloads.

“Russian fighter crews identified the aerial targets as two U.S. Air Force supersonic strategic B-1B bombers, accompanied by two KC-135 refuelling planes, and escorted them over the waters of the Black Sea,” the defence ministry said in a statement accompanied by video footage of the U.S. aircraft in flight.

“After the foreign warplanes had been turned away from Russia’s state border, the Russian fighters safely returned to their home air base.”

It said the Russian aircraft had carried out their flight in strict compliance with international airspace rules and that Russia’s borders had not been breached.

Visiting Ukraine on Tuesday, Lloyd Austin, the U.S. defense secretary, said that Russia was an obstacle to peace in eastern Ukraine and called on Moscow to end destabilising activities in the Black Sea and along Ukraine’s borders.

Moscow blames Kyiv for a lack of progress in implementing a peace deal covering eastern Ukraine, something Ukraine denies.

A similar incident with a B-1B occurred on Sunday over the Sea of Japan, just days after an incident with a U.S. naval destroyer, also in the far east.

B-1B bombers are being used in a series of exercises with NATO allies across Europe encompassing the Arctic, the Baltics and the Black Sea, Air Force Magazine reported earlier this month.