(Bloomberg) -- Kazakhstan has filed a claim against the giant Kashagan oil venture for about 2.3 trillion tenge ($5.1 billion) in environmental protection fines, according to the Ecology and Natural Resources Ministry.

The ministry accuses the North Caspian Operating Company, which runs Kashagan, of keeping more than double the amount of sulfur permitted on the site, the ministry said in response to questions from Bloomberg. 

NCOC didn’t immediately respond to a request for comment. Earlier this month, the operator said it manages “production and storage of sulfur responsibly, and in accordance with the requirements of the legislation of the Republic of Kazakhstan, as well as in accordance with applicable standards and best practices.”

Kazakhstan is Central Asia’s largest energy producer and an increasingly important alternative to Russian crude supplies for Europe since the invasion of Ukraine. In Kashagan, companies have invested more than $50 billion. The partners in the development are Shell Plc, Exxon Mobil Corp., Eni SpA, TotalEnergies SE, China National Petroleum Corp., and Inpex Corp. as well as Kazakhstan’s state-run KazMunayGas National Co.

The demand for the environmental fine comes as Kazakhstan is looking for ways to assert greater control over NCOC, a person close to the project said earlier this month.

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