"Today the Russian finance ministry filed the lawsuit against Ukraine with the goal of recovering debt on Ukraine's bond with the nominal value of USD 3 billion," Finance Minister Anton Siluanov was quoted by Russian news agencies as saying.

Siluanov predicted that the court case will be "open and transparent" at the "independent, authoritative court which will examine the dispute impartially.

Moscow and Kiev have been locked in a protracted standoff over the USD 3 billion that the Kremlin gave to Ukraine in 2013 shortly before former Russia-backed President Viktor Yanukovych fled the country in the wake of mass protests.

Kiev argues that Moscow lent its ally the money on preferential terms essentially as a bribe for Yanukovych's shock November 2013 decision to scuttle a free trade agreement with the EU that Kiev has since signed.

The new government wants Russia to accept a 20-percent debt write down - the same terms accepted last year by Ukraine's private creditors.

Ukrainian authorities insist that the funds do not represent a sovereign loan granted by one state to another, but rather a transaction made via the financial markets and subject to financial terms agreed with other creditors.

The debt dispute between Moscow and Kiev has previously threatened to hamper the International Monetary Fund's USD 17.5-billion rescue plan for cash-strapped Ukraine.

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