A Russian tanker was damaged in a Ukrainian drone attack in the Kerch Strait, briefly halting traffic on the strategic bridge linking Crimea to Russia on Saturday, a day after one of Moscow's warships was hit in the Black Sea.

The number of attacks in the Black Sea has increased from both sides since Moscow exited a deal last month that had allowed Ukrainian grain exports via the shipping hub during the conflict between the two countries.

The Russian tanker SIG was hit around 11:20 pm (2020 GMT) Friday south of the Kerch Strait, Russia's Federal Agency for Sea and Inland Water Transport said.

The SIG suffered a hole at the waterline in the area of the engine room, "presumably as a result of an attack by a marine drone", the agency said on Telegram. "The ship is afloat."

An oil boom had been placed around the vessel and preparations were under way to patch the damage, it said.

The Marine Traffic vessel-tracking website showed the SIG stationary and attended by tugs just south of the strait.

The oil and chemical tanker is under US sanctions for supplying jet fuel to Russian forces in Syria supporting President Bashar al-Assad.

Russia's state RIA Novosti news agency said there were no casualties in the attack, citing the Maritime Rescue Coordination Centre of Novorossiysk.

Traffic on the bridge across the Kerch Strait linking the Moscow-annexed Crimean peninsula to Russia's mainland was halted for around three hours and resumed early Saturday, according to the Russian highways information centre's Telegram channel.

- Warship hit -

The latest attack in the Black Sea came a day after Ukraine said it had carried out a seaborne-drone strike on a Russian navy ship at Novorossiysk naval base in southern Russia.

In a video of the purported attack on the warship obtained by AFP, a naval drone is seen speeding towards the darkened silhouette of a military vessel before the connection abruptly cuts off.

A Ukrainian attack targeting the Olenegrorsky Gornyak landing ship was "successful", a Ukrainian security source told AFP Friday.

"The goal was to show that Ukraine can attack any Russian warship in that zone," the source added.

Russia said it had repelled an attempted attack on the naval base by the Ukrainian armed forces "with the use of two unmanned sea boats".

Russia's Black Sea Fleet has been targeted since the beginning of Moscow's military campaign in Ukraine more than a year ago, but attacks have increased in recent weeks.

"Another Russian ship is on the edge of its fall," the Ukrainian foreign ministry said on social media, alongside a video of a military vessel listing heavily to one side. 

"The presence of the Russian fleet in the Black Sea... will be put to an end," Ukrainian presidential aide Mykhailo Podolyak said.

"Ukraine will ensure freedom and security in the Black Sea for world trade."

The port of Novorossiysk also hosts the terminus of a pipeline that carries most Kazakh oil exports through Russia.

The fuel artery's operator Caspian Pipeline Consortium said it was continuing to ship oil to moored tankers at the terminal, Russian state media reported Friday.

- Crimea attack -

Crimea, annexed by Russia in 2014, has been targeted by Kyiv throughout Moscow's Ukraine offensive but has seen more intense attacks in recent weeks.

Ukrainian drone strikes on Crimea in July blew up an ammunition depot and damaged the strategic bridge across the Kerch Strait.

The Russian defence ministry on Friday said it had downed 13 drones over the Crimean peninsula, without recording casualties or damage.

Earlier this week, Russia's defence ministry said it foiled a Ukrainian drone attack targeting patrol boats in the Black Sea.

Also announced Friday was Russian Defence Minister Sergei Shoigu's visit to a combat zone in Ukraine to inspect a command post and meet senior military officers.

Shoigu got an update on the situation on the front and "thanked commanders and soldiers... for successful offensive operations" in Lyman in eastern Ukraine, the army said, without mentioning when the visit took place.

- Ukraine counteroffensive -

Shoigu last visited the front at the end of June after an aborted rebellion by the Russian paramilitary group Wagner fighting along with Moscow's forces in Ukraine.

Ukraine began its long-awaited counteroffensive in the same month but has made modest advances in the face of stiff resistance from Russian forces on the front line.

Ukrainian President Volodymyr Zelensky said Thursday that the counteroffensive was difficult, reporting "very violent" fighting in the key areas on the eastern and southern fronts.

Late summer and early autumn 2022, Ukraine retook swathes of territory around Kherson and Kharkiv in rapid counteroffensives.

But Ukrainian forces are now contending with well-entrenched Russian defensive positions built over several months.

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