Ukraine says it sank a $300 million Russian submarine in what could be another big blow to Putin's Black Sea Fleet

• Ukraine says it sank a Russian Black Sea Fleet submarine in Crimea.
• The Kilo-class submarine Rostov-on-Don was hit in Sevastopol, Ukraine's military said.
• Ukraine has relentlessly targeted Russia's Black Sea Fleet since the war began.

Ukraine says it struck and sank a Russian Black Sea Fleet submarine and damaged a number of prized S-400 air defense systems in Crimea.

In a statement on Telegram, the General Staff of the Ukrainian Armed Forces said the Kilo-class submarine Rostov-on-Don was hit in the port of Sevastopol.

"The boat sank on the spot," the General Staff said.

"The destruction of the Rostov-on-Don proves once again that there is no safe place for the Russian fleet in the Ukrainian territorial waters of the Black Sea," it added.

Business Insider was unable to independently verify the claim. The Russian Defense Ministry has not yet commented.

The Russian-appointed governor of Sevastopol, Mikhail Razvozhayev, posted on Telegram on Sunday morning but did not reference Ukraine's announcement.

"Everything is quiet in the city," he wrote, while also warning of an upcoming training exercise.

Ukraine's military said the B-237 Rostov-on-Don "is one of four Kilo-class submarines capable of using 'Kalibr' missiles."

It is not the first time that sub, which Ukraine says cost Russia $300 million, has been targeted in the conflict.

The UK's Ministry of Defence (MoD) said in September that the submarine had "likely suffered catastrophic damage" following a missile strike on a shipyard in Sevastopol.

"Any effort to return the submarine to service is likely to take many years and cost hundreds of millions of dollars," the MoD said at the time.

Despite having no traditional navy of its own, Ukraine has had huge success battling the Black Sea Fleet.

Many of the fleet's ships have been forced to relocate eastward from the naval base in Sevastopol to Novorossiysk, and it has also lost a number of key warships, including its flagship, the Moskva.

In addition to striking the submarine, the General Staff said Ukrainian forces had also severely damaged four S-400 antiaircraft missile launchers.

Frederik Mertens, a former strategic analyst at the Hague Centre for Strategic Studies, previously told BI that by targeting Crimea and defense systems such as the S-400 , Ukraine was likely "preparing the ground" for the use of F-16 fighter jets, which arrived in Ukraine earlier this week.