Online Desk : Oil that leaked from two stricken tankers off the Russian coast has been detected on more beaches on the annexed peninsula of Crimea, Russian authorities said, as volunteers mount a massive environmental cleanup operation.

Two ageing Russian tankers -- the Volgoneft-212 and the Volgoneft-239 -- were hit last month by a storm in the Kerch Strait, which links the Azov and Black Seas between Moscow-annexed Crimea and the southern Krasnodar region.

They were carrying 9,200 tonnes of heavy fuel oil, around 40 percent of which may have spilled into the sea, in what President Vladimir Putin called an "ecological disaster," reports AFP.

"Two sites of oil product pollution were detected in Crimea," Russia`s emergency situations ministry said Thursday.

They were near the beach in the city of Kerch and further south near the Tobechytske lake.

Almost 73,000 tonnes of contaminated sand has been removed from dozens of kilometres of beaches on the Russian coast since the spill, the ministry said Thursday.

Some 200,000 tonnes of sand and soil could have been contaminated in total, officials have said.

The regional headquarters overseeing the cleanup published images of volunteers in white suits scooping contaminated sand off beaches with shovels, including in the popular resort city of Anapa.

It said Thursday that 2,100 birds had been rescued so far.

Russian scientists last month criticised the cleanup, saying volunteers did not have the right equipment.

Ukraine has called the oil spill "the largest in the Black Sea region in the 21st century" and blamed Moscow for using ships unsuitable for harsh winter conditions.

Under Western sanctions, Russia has resorted to using a so-called "shadow fleet" of mostly old tankers to export its fuels around the world.

"Most of the more than 1,000 tankers of the Russian `shadow fleet` are hopelessly outdated, have fictitious insurance policies, conceal their true owners, and often overload oil at sea. Other large-scale accidents are statistically inevitable," Mykhailo Podolyak, an advisor to Ukrainian President Volodymyr Zelensky, said last month.