Russia's Defence Ministry said on Wednesday that the Russian warship Ivan Hurs had been attacked unsuccessfully by three Ukrainian uncrewed speedboats in the Black Sea, on the approaches to the Bosphorus strait.
In a statement posted on Telegram, the ministry said the warship had been protecting the TurkStream and Blue Stream gas pipelines - which carry gas from Russia to Turkey, partly across the Black Sea - and "continues to fulfill its tasks."
No comment was immediately available from Kyiv.
The ministry cited the attack as a justification for Russia expanding defensive measures. Explosions last September damaged the Nord Stream 1 and 2 pipelines bringing gas from Russia under the Baltic Sea to Germany.
Rising tensions in the Black Sea
The Russian statement appeared likely to raise tensions in the Black Sea, where Russia only agreed last week, one day before deadline, to extend a deal allowing Ukraine to export grain safely from its seaports.
TurkStream carries gas from Russia's Taman peninsula west across the width of the Black Sea to a point west of the Bosphorus.
Blue Stream, however, crosses the eastern Black Sea from north to south, making landfall more than 700 km east of the Bosphorus.
"All enemy boats were destroyed by fire from the standard armament of a Russian ship 140 km northeast of the Bosphorus," the statement added.
The Ivan Hurs is a medium reconnaissance ship launched in 2013.