Ukraine said Monday it has killed the in a in occupied Crimea.
It comes days after an attack that left the building smoldering, the latest salvo in a mounting effort to target the Kremlin's naval forces and isolate the annexed peninsula.
Kyiv did not provide evidence for the claim, which NBC News has not verified, but if confirmed it would be one of the most high-profile losses of the war so far.
Ukraine's Special Operations Forces said in a post on Telegram that "the commander" of the Black Sea Fleet was among 34 officers who died in the strike on the fleet's headquarters in the Crimean city of Sevastopol on Friday.
The commander of the fleet is Viktor Sokolov, although the Ukrainian statement did not name him directly.
Rumors had circulated among Ukraine-watchers all weekend that Sokolov had been killed. NBC News has contacted Russia's defense ministry for comment.
"If true it would likely be the highest ranking naval officer killed in combat since WWII," Admiral James Stavridis, former NATO supreme allied commander and current chief international security analyst for NBC News, posted on X, formerly known as Twitter.
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On Saturday, Ukraine's Special Operations Forces said in another Telegram post that the strike on the fleet's headquarters caused "dozens of dead and wounded occupants, including the senior leadership of the fleet."
It said the strike had been part of an operation named "Crab trap" that it said was carried out "on time and accurately" during a meeting of the Russian navy's senior members at the building.
Ukraine's intelligence chief, Kyrylo Budanov, told Voice of America on Saturday that at least nine people were killed and 16 others wounded as a result of Kyiv's attack on the Black Sea Fleet on Friday. He said Alexander Romanchuk, a Russian general commanding forces along the key southeastern front line, was "in a very serious condition" following the attack.
Shortly after Friday's attack, Russia's defense ministry said that one serviceman was killed. It later said this person was missing, adding that five missiles were shot down by air defenses.
Russia annexed Ukraine's Crimea in 2014, in violation of international law.
It has since bolstered the peninsula's military assets, but its use of the area just off Ukraine's mainland coast to support its invasion has also made it a growing target for Kyiv's strikes.
Ukraine's efforts to hit behind Russian lines were given a boost last week when President Joe Biden told President Volodymyr Zelenskyy the U.S. would provide a small number of long-range Army Tactical Missile Systems, known as ATACMS, three U.S. officials and a congressional official familiar with the discussions told NBC News.
Ukraine has vowed it will retake Crimea as part of its campaign and has stepped up its attacks against the Russian navy in recent months, damaging ships and buildings stationed on the peninsula.
Sevastopol, the city hit by Friday's strikes, is the largest population center in Crimea. Its port is the main base of the Black Sea Fleet, which has been used to launch attacks deep into Ukraine.
In April last year, Ukrainian missiles launched with the help of U.S. intelligence sank a Russian guided missile cruiser, the Moskva, which was the flagship of the fleet and the largest Russian warship sunk in combat since World War II.
Sokolov has led the fleet since August last year, the result of a major reshuffle that came after the Moskva's sinking and strikes against the fleet on Crimea.
He rose through a series of posts in the Pacific and Northern Fleets, serving as deputy commander in the latter, according to Russian state media. From 2020 he headed a prestigious military academy, before taking command of the Black Sea Fleet last year.
— The Associated Press and Daryna Mayer contributed.
