Ukrainian drones struck eight tankers from Russia's so-called "shadow fleet" that weredelivering fuel to Crimea overnight, Kyiv's military said on Tuesday, part of a mounting effort to isolate the Russian-occupied peninsula.

In a statement on Telegram, Ukraine's drone forces said they had struck the vessels - each under international sanctions and with a deadweight of around 7,000 tons - in the Sea of Azov. It came a day after the same forces said they had hit two other shadow-fleet vessels around the same area.

Ukraine has stepped up attacks on logistics and energy infrastructure in Crimea in recent weeks, sparking fuel shortages and a state of emergency in the territory, which is critical to Russia's war on its smaller neighbour, now in its fifth year. Russia annexed Crimea in 2014, ahead of its full-scale invasion in 2022.

"Striking the enemy's naval logistics complicates the supply of fuel and ammunition necessary to support the activities of Russian troops, primarily in the temporarily occupied territory of Crimea," the drone forces said.

The unit posted black-and-white, drone-view footage showing ships being targeted and erupting into flames. Reuters could not independently verify the information. Kyiv has long urged its international allies to crack down on vessels skirting sanctions by delivering Russian oil to international markets.

Ukrainian forces have attacked with sea drones to disable some tankers transporting Russian oil in the Black Sea, part of a campaign to reduce Moscow's revenue streams. There have also been a series of unexplained blasts on tankers that have called at Russian ports.

Ukraine has not confirmed or denied its role in those attacks, though maritime security sources suspect Ukraine is behind them.