KazMunayGas said it had cleaned up nearly 363,000 cubic metres (12.8 million cubic feet) of oil waste in the last four years at the Karazhanbas field in the western Mangystau region on the coast of the vast inland sea.

Reclamation work included cleaning contaminated soil and above-ground storage facilities, the company said in a statement.

The Caspian Sea, which is surrounded by Azerbaijan, Iran, Kazakhstan, Russia and Turkmenistan, is also described as the world's biggest lake, stretching over 371,000 square kilometres (143,000 square miles).

Resource-rich Kazakhstan has been hit by pollution from the oil and gas industry and the authorities in Almaty are mulling the creation of "environmental disaster zones" in several regions.

In Central Asia, work to remove toxic waste dating back to Soviet times has gathered pace in recent years, particularly in Tajikistan and Kyrgyzstan, where millions of cubic metres of radioactive waste are stored.