One of Russia's biggest oil tankers was struck by a maritime drone, the latest salvo in a Ukrainian military campaign employing unmanned vehicles to attack far-away Russian targets by air and by sea.

The Russian-flagged ship, the Sig, was hit by a drone carrying 450 kilograms (992 pounds) of TNT shortly before midnight, according to a Ukraine Security Service source. The strike created a hole in the vessel's engine room at the waterline on the starboard side, forcing the 11-strong crew to fight the water intake, Russian authorities said. The flooding eventually stopped.

Russia's Federal Agency for Marine and River Transport said no casualties were reported and that the Sig was not carrying oil when the drone crashed into ship. Ukrainian officials, however, said some crew were injured and that the tanker was carrying fuel for the Russian military.

CNN has not been able to independently verify the claims.

The strike on the Sig came just hours after Ukrainian sea drones targeted a major naval base in Novorossiysk, a coastal city on the Black Sea that is home to Russia's largest port by volume of cargo handled. An amphibious Russian landing ship was hit, leaving it tilting badly and sitting very low in the water.

Ukrainian has also stepped up its attacks using unmanned aerial vehicles in recent weeks, hitting targets well within Russian territory, including in Moscow.

The two sea-based attacks Friday took place near the Kerch Strait, which connects the Crimean Peninsula to mainland Russia.

After illegally annexing the peninsula in 2014, the Kremlin spent around $3.7 billion to both physically and symbolically connect Crimea to Russia by bridge. Russian President Vladimir Putin personally led a convoy over the 12-mile overpass -- Europe's longest -- to celebrate its opening in 2018.

The Kerch Bridge has been targeted several times since Russia invaded Ukraine last year. An explosion in October killed three people and collapsed part of the roadway and Ukrainian forces attacked the bridge last month.

Friday's assault, however, appeared to be one of the biggest to date. In addition to the attacks on the Sig and the naval base, Friday morning saw Ukrainian aerial drones target an oil storage facility in Feodosia, a town on the Crimean Peninsula's south coast. Ten unmanned aerial vehicles in total were downed over Crimea, according to Russia's Defense Ministry

Ukrainian authorities have vowed to continue targeting the bridge and ships navigating Ukrainian territorial waters, even if they are controlled by Russia. The head of the Ukrainian Security Service, Vasyl Maliuk, called such attacks "absolutely logical and effective."

Maliuk said that if the Russians wanted such incidents to stop, "they have the only option to do so -- to leave the territorial waters of Ukraine and our land."