In the first direct US-Russian incident since the start of the Ukraine war, a Russian Su-27 jet struck the propeller of the unmanned MQ-9 drone, rendering it inoperable, according to the Pentagon, worsening already strained relations between Washington and Moscow

The top US general said on Wednesday that a US surveillance drone brought down over the Black Sea after a Russian military intercept probably broke apart and would be difficult to recover given the depth of the water in the area.

In the first direct US-Russian incident since the start of the Ukraine war, a Russian Su-27 jet struck the propeller of the unmanned MQ-9 drone, rendering it inoperable, according to the Pentagon, worsening already strained relations between Washington and Moscow.

The crash was caused by “sharp manoeuvring” by the drone, according to Russia's defence ministry, and its jet did not make contact.

“It probably sank to some significant depths, so any recovery operation from a technical standpoint would be very difficult,” said General Mark Milley, Chairman of the Joint Chiefs of Staff.

Milley warned that it would take several days for the US to know for certain the size of the debris field in waters as deep as 4,000 to 5,000 feet (1,219 to 1,524 metres).

Russia said on Wednesday that it would try to recover the drone's remains, but acknowledged the difficulties.

“I'm not sure if we'll be able to retrieve it, but it needs to be done. And we will undoubtedly work on it. Of course, I hope for success,” Nikolai Patrushev, Secretary of the Kremlin Security Council, told the Rossiya-1 TV channel.

Milley stated that the US had already taken precautions to avoid the loss of sensitive intelligence if the drone was recovered by Russia.

“We're quite certain that whatever was valuable is no longer valuable,” Milley said.