According to Ukrinform, the UK Ministry of Defense said this in its latest intelligence update posted on Twitter.
"The Bosporus Strait remains closed to all non-Turkish warships, rendering Russia unable to replace its lost cruiser Moskva in the Black Sea," the ministry said.
It added that despite the embarrassing losses of the landing ship Saratov and cruiser Moskva, Russia's Black Sea Fleet retains the ability to strike Ukrainian and coastal targets.
"Approximately 20 Russian Navy vessels are currently in the Black Sea operational zone, including submarines," the ministry said.
A full-scale Russian invasion of Ukraine has been going on since February 24.
On February 27, Turkey announced the closure of the Bosphorus and Dardanelles to warships in accordance with the provisions of the Montreux Convention.
On March 24, Ukrainian troops destroyed the Russian landing ship Saratov in the port of Beridiansk.
On April 13, the Ukrainian military hit the Russian cruiser Moskva from the Neptune anti-ship missile system, causing serious damage to the warship. Russia confirmed later that the cruiser sank while being towed to its destination.
