The Central Asian country has stepped up fines on environmental violators in recent years, as it seeks to placate concerns about pollution while also exploiting its immense natural resources.

The North Caspian Operating Company -- a group that includes Shell, Exxon Mobil, China's CNPC and TotalEnergies -- was fined 3.5 billion tenge ($6.6 million) in damages "for excessive unauthorised flaring" at the vast Kashagan oilfield, Astana's court service said.

Flaring is the burning off of excess gas that comes from the ground during oil drilling.

It is carried out for safety reasons but the process often releases harmful environmental pollutants into the air.

The Kashagan oil reservoir is one of the largest oil discoveries in recent decades, containing the equivalent of about nine to 13 billion barrels of recoverable oil, according to the North Caspian Operating Company.

The Caspian Sea is particularly sensitive to pollution, with shrinking water levels, waste from oil extraction and agricultural run-off all contributing to habitat loss.