LONDON (Reuters) - Blasts at the Saky air base in the annexed Crimean peninsula earlier this month have put more than half of the Russian Black Sea fleet's naval aviation combat jets out of use, a Western official said on Friday.

The air base near Novofedorivka on the west coast of the peninsula, which Russia annexed from Ukraine in 2014, suffered multiple explosions on Aug. 9.

The official, speaking on condition of anonymity, said Ukraine was now consistently achieving "kinetic effects" deep behind Russia's lines which was having a material impact on Russia's logistics support and "a significant psychological effect on the Russian leadership".

"We now assess that the events of Saky airfield on August 9 put more than half of Black Sea fleet's naval aviation combat jets out of use," the official said.

On Aug. 12, Britain's Ministry of Defence said in its intelligence update that while a fraction of Russia's air fleet was destroyed in the blast, the navy's air capability was seriously degraded.

The official said the Black Sea fleet was struggling to function much more than "a coast defence flotilla" which just occasionally conducted missile strikes, and that its attempt to threaten amphibious assault on Odessa had been stymied.

The official added that overall, the war was at a "moment of near operational standstill".

"Neither side's ground forces have sufficient concentrated ground combat power to launch effective offensive actions which would in any way materially affect the course of war," the official said.

(Reporting by Michael Holden; Editing by Tomasz Janowski)