According to the sources, the patrol boat was engaged in counter-drone operations at the time of the strike. It was hit while operating in Crimea.
The strike was reportedly carried out by an FPV drone equipped with an enhanced warhead, the sources said.
Explosions were reported across occupied Crimea overnight on June 4. Local residents reported a series of blasts and air defense activity in occupied Sevastopol and Simferopol, as well as near the Hvardiiske, Belbek and Saky airfields.
Mikhail Razvozhayev, the Russian-installed governor of Sevastopol, confirmed the drone attack and claimed local air defenses had shot down seven drones over the Nakhimov district, the North Side area and Victory Park.
On June 3, Ukraine's Defense Forces struck two Russian vessels during an attack on St. Petersburg. Ukraine's Security Service (SBU) later confirmed that a military ship anchorage in Kronstadt had been targeted.
The extent of the damage and the results of the strike are still being assessed, the SBU said.
Earlier, sources told NV that Ukraine's Defense Forces had struck a Russian patrol corvette in St. Petersburg that was likely involved in protecting tankers belonging to Russia's so-called shadow fleet. The vessel was targeted during the attack on the Kronstadt naval base.