Naftogaz, the Ukrainian state-owned energy company, has filed a lawsuit against Russia in the US court system, seeking $5 billion in compensation for damages and property it lost in Crimea, according to a statement by the company released on Friday.

Previously at The Hague, an arbitration panel had awarded Naftogaz compensation “equal to the fair market value”  of the assets of the company which were lost in Crimea when the peninsula joined with Russia.

Naftogaz CEO Aleksey Chernyshov said, “Since Russia has not voluntarily paid the funds to Naftogaz as provided for by the award, we intend to leverage all available mechanisms to recover these funds.” The statement noted that the company had filed a claim with the US District Court for the District of Columbia.

Naftogaz was one of six Ukrainian oil and gas firms which engaged arbitration proceedings against Russia in October of 2016. Naftogaz estimated the assets it had lost in Crimea to be worth $5 billion. In March of 2022, hearings to determine the value of the compensation which was owed ended. In April Russia issued a statement it was analyzing the ruling of The Hague, and would decide on further steps.

Following a referendum in 2014, Crimea joined with Russia following a coup in the rest of the country which overthrew the democratically elected leader, whom Crimea supported. The western powers, including The EU, the US, and a number of other nations, called the move an “illegal annexation” by Russia and began a long process of imposing ever more stringent sanctions on Moscow.

In 2018 Russian state-owned energy giant Gazprom was ordered by the Stockholm Arbitration Court to pay Naftogaz $2.6 billion following a four-year legal battle over gas supply contracts. Gazprom honored the ruling.