Blasts this week at the Russian-operated Saky military airfield in western Crimea led to the loss of eight Russian combat jets, degrading its navy's Black Sea aviation fleet, Britain said on Friday.
While the damaged jets are only a fraction of the overall aviation fleet, Britain said Black Sea capability would be affected, since Saky is used as a primary operational base.
The base airfield probably remained operational, but its dispersal area had suffered serious damage, Britain's defence ministry added in a regular intelligence bulletin on Twitter.
The explosions, which Russia has said killed one and injured five, will prompt its military to revise the threat perception in the region, the ministry added.