The United States military was forced to essentially crash its MQ-9 Reaper surveillance drone because of the damage caused when it was struck by a Russian jet, the Pentagon said on Tuesday.

"Because of the damage, we were in a position to have to essentially crash into the Black Sea," Brigadier General Pat Ryder told reporters, adding that the drone was basically unflyable after the damage.

Ryder said Russia had not recovered the crashed drone at this point.