Russia has filed a lawsuit against Ukraine at London’s High Court over a $3bn (£2.1bn) debt.
The action was taken following unsuccessful attempts to agree on a debt restructuring, Russian Finance Minister Anton Siluanov has said.
Ukraine announced in December that it would not make the repayment, claiming that Russia had refused to accept terms offered to other creditors.
The countries have been at loggerheads since Russia annexed Crimea in 2014.
The $3bn eurobond had a maturity date of 20 December of last year. It was issued in late 2013, shortly before pro-Russian President Viktor Yanukovych was removed from power following massive protests.
But just days before its due date, Ukraine’s Prime Minister, Arseny Yatsenyuk, said that the country had imposed a moratorium on the repayment.
At the time, Mr Yatsenyuk said the moratorium would be in place until the acceptance of Ukraine’s restructuring proposals or the adoption of the relevant court decision.
Mr Siluanov said he hoped the legal case will be “open and transparent” at the “independent, authoritative court”.
“The lawsuit was filed after repeated unsuccessful attempts to engage Ukraine in a constructive dialogue on debt restructuring,” he said.
Tensions have been running high between the two neighbours. Kiev and the West have accused Moscow of arming and aiding separatist rebels in eastern Ukraine, allegations that Russia has denied.
The two countries have been embroiled in disputes over gas supplies and commerce following Ukraine’s decision to join an EU free trade agreement.