A Russian attack targeted port infrastructure in Ukraine's Izmail district in the southern region of Odessa overnight, Ukrainian authorities said on Monday.
Fires caused by the attack have been extinguished, the authorities added on a social media messaging platform.
Russia's defence ministry said its forces had hit military targets in the port, which it described as "a berthing terminal used for unloading vessels carrying military cargo, hangars housing Western military equipment, and depots for naval drones". Reuters could not verify the ministry's assertions.
Izmail, close to the Romanian border, is home to Ukraine's largest port on the Danube river.
In a separate strike, Russia said its forces had hit a patrol boat and fuel storage tanks in Odessa.
The local governor there said a civilian Togo-flagged vessel was damaged and four people were injured.
(Reporting by Anna Pruchnicka in Gdansk and Anastasia Teterevleva in Moscow; Editing by Clarence Fernandez and Emelia Sithole-Matarise)