Kyiv has not commented on the attack, which would be a rare successful hit on a Russian “shadow fleet” vessel while it was some 2,000 kilometres (1,200 miles) from Ukraine.
The Libyan port authority said the Russian carrier, Arctic Metagaz, sank after “sudden explosions” north of the port of Sirte.
The ship “had experienced sudden explosions followed by a massive fire, which ultimately led to its complete sinking” on Tuesday night, it said.
Moscow said the tanker had been attacked by Ukrainian naval drones in “an act of international terrorism and maritime piracy”.
The Russian transport ministry said the strike “was launched from the Libyan coast by Ukrainian naval drones,” without providing more details.
There has been no immediate comment from Ukrainian officials on the accusations.
Ukraine in December said it had hit a Russian tanker with aerial drones in the neutral waters of the Mediterranean Sea, in what was the first such strike there in the now four-year war.
The Arctic Metagaz had been sanctioned by the United States and the European Union as part of Russia’s fleet of ageing tankers that carry oil and gas exports around the world, skirting Western restrictions.
Unverified footage and photos circulating on social media since Tuesday night showed a massive explosion out at sea.
The Libyan port authority said the ship was carrying an estimated 62,000 metric tons of liquefied natural gas (LNG) on its way to Port Said, Egypt.
The Russian ministry said it had departed from the northern Russian port of Murmansk.
All 30 crew members have been rescued, Moscow said. Two received burns, Russian state media reported, citing the transport ministry.
The Libyan port authority said the wreckage took place between Libya and Malta “within the Libyan search-and-rescue zone… approximately 130 nautical miles (240 kilometres) north of the port of Sirte”.
It warned all ships against approaching the wreckage site, citing the risks of collision and security concerns.
The Libyan National Oil Corporation said in a statement the carrier was only transiting through the central Mediterranean and had “nothing to do” with it.
“Traffic in Libyan ports continues normally and regularly,” it said, adding that the incident had “no impact on the flow of oil and gas supplies or the supply of fuel to the local market”.
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