A Ukrainian sea drone pictured before it allegedly hit a Russian navy ship and exploded
This is the latest of the increasingly frequent attacks in the Black Sea since Moscow exited a deal last month that had allowed Ukrainian grain exports there.
"Overnight the (Ukrainian Security Service) SBU blew up the 'SIG', a large oil tanker of the Russian Federation that was transporting fuel for Russian troops," the security source said.
It added that the "successful special operation", which involved a naval drone and explosives, was carried out jointly with the Navy on Ukrainian territorial waters.
The source described the targeted vessel as "one of the most powerful oil tankers of the Russian Federation."
"It was well-loaded with fuel, so the 'fireworks' could be seen from afar," the source added.
Russian authorities said the SIG tanker was hit around 11:20 pm (2020 GMT) Friday south of the Kerch 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.