The storied Russian warship Moskva, whose proud history goes back to days of the Cold War, sank into the Black Sea on Thursday in the latest blow to Moscow's war effort in Ukraine. 

Losing the vessel, built in Ukraine during the Soviet era and named after the Russian capital, represents a major military setback and symbolic defeat for Russia as its troops regroup for a renewed offensive in eastern Ukraine after stumbling in the north.

The Russian Defense Ministry said the Moskva -- flagship of the country's Black Sea fleet -- was being towed to port when it "lost its stability due to damage to the hull received during the fire from the detonation of ammunition. In the conditions of stormy seas, the ship sank." The crew, usually totaling about 500, had been evacuated, the ministry said.

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The Pentagon couldn't confirm the source of the damage, but Odesa Gov. Maksym Marchenko said on Telegram that Ukrainian forces struck the guided-missile cruiser with two missiles. Oleksiy Arestovych, an adviser to Ukraine's president, called the ship's sinking an event of “colossal significance."

U.S. national security adviser Jake Sullivan said it mattered little whether the ship was hit by a missile or victimized by an unrelated fire.

“They’ve had to kind of choose between two stories: One story is that it was just incompetence, and the other was that they came under attack," Sullivan said. "Neither is a particularly good outcome for them."