"The volume of polluted soil could reach 200,000 tonnes," Alexander Kozlov said at a meeting broadcast by the Zvezda channel on Telegram.

On December 15, two Russian oil tankers, the Volgoneft-212 and the Volgoneft-239 were hit by a storm in the Kerch Strait, with one sinking and the other running aground.

The strait separates southern Russia from the Ukrainian peninsula of Crimea, which it annexed in 2014.

The ships were carrying 9,200 tonnes of fuel oil, around 40 percent of which may have spilled into the sea, according to Russian authorities.

President Vladimir Putin last week called it an "ecological disaster".

Fuel oil was found along dozens of kilometres of beach, with the seaside resort of Anapa particularly hard hit.

The port city of Kerch, in annexed Crimea, also saw patches of fuel oil arrive on its shores, according to images broadcast by local authorities.

Volunteers in white protective clothing have been clearing up beaches in the region, according to images published on Monday by regional governor Veniamin Kondratyev.

"Volunteers said that last night almost everything had been cleaned up, but during the night the waves deposited fuel oil again," he said.

Local authorities also broadcast images of oil-spattered birds being treated by volunteers.

Ten dolphins may also have been killed by the oil spill, the specialist Delpha centre said on Sunday, adding that tests were needed to confirm the cause of death.

"This is an extremely alarming situation," the scientific institution, which protects dolphins in the Black Sea, said on Telegram.