Ukrainian forces have reportedly struck and damaged another Russian warship in the waters off Crimea. Russia denies the claim.
Ukrainian media outlets have cited security service sources in the country as saying that the attack occurred on Thursday.
They have reported that a maritime drone struck a missile corvette of the Russian Black Sea Fleet off the military port city of Sevastopol. They say the vessel's rear right side sustained "significant damage."
The Russian defense ministry said on Thursday that the attack was repelled. It claimed that the corvette destroyed an unmanned boat that belonged to Ukraine.
Ukraine has been increasing its attacks on the Black Sea Fleet in the waters around Crimea, the southern peninsula unilaterally annexed by Russia in 2014.
The Ukrainian military said it damaged a Russian landing ship and a submarine on Wednesday. It added that it carried out a maritime drone attack on two patrol vessels on Thursday.
US TV network CNN has cited a Ukrainian source familiar with the country's strategy as saying that strikes on Crimea are an integral part of Ukraine's counteroffensive.
The source reportedly said that the attacks are "intended to try to isolate the peninsula and make it more difficult for Russia to sustain its military operations on the Ukrainian mainland."