Russia has fitted submarines at a key Black Sea facility with anti-drone cages in a bid to shield them from Ukrainian long-range attacks, based on a fresh Western intelligence report.

The British defense ministry reported on Friday that satellite photos from June 6 to 9 showed these protective cages over the conning towers of three Kilo-class submarines docked at the Novorossiysk naval base.

Britain assessed it as almost certain that a fourth submarine there will get the same treatment soon. One satellite image released by the ministry displayed two of the boats already covered by the structures.

As part of its regular update on the invasion, Britain described the work as almost certainly a precaution against Ukraine's growing capacity to hit distant targets using drones.

Russia's defense ministry and its embassy in the US offered no immediate reply to requests for comment on the British findings.

Novorossiysk now serves as the main hub for Russia's Black Sea Fleet after repeated Ukrainian strikes earlier in the conflict pushed Moscow to relocate vessels and equipment away from its former base in Sevastopol on occupied Crimea.

Ukraine has launched multiple drone assaults on the Novorossiysk site, including with explosive uncrewed surface vessels. Russia has responded with water barriers, while the new cages mark fresh steps to guard submarines even though they mainly address threats from the air.

Cage armor appears often in combat zones to shield tanks and other vehicles from small drones or fragments. Applying it to a vessel, particularly a submarine, remains uncommon.

Similar anti-drone netting protects infrastructure including supply routes close to the front in Ukraine as well as energy sites and arms factories inside Russia.

Britain's review of the Novorossiysk cages arrives as Ukraine steps up long-range missile and drone operations deep into Russian territory.

Officials in Kyiv often call this effort long-range sanctions and have focused it mainly on energy targets. On Tuesday Kyiv stated it conducted over a dozen such strikes during June.