Ukraine missiles and drones hit the Novorossiysk where Russia's Black Sea fleet took refuge after repeated attacks on its Crimea base, reports said.
Ukrainian drones hit Novorossiysk port, causing a fire and power outages, reports say.
The attack follows heightened defenses at the port after previous Ukrainian strikes on Crimea.
Novorossiysk is vital for Russia's oil exports and naval operations in the Black Sea.
The Russian port of Novorossiysk, which has become an important base for the Black Sea Fleet after repeated attacks on its traditional base in Crimea, has been targeted by Ukrainian drones.