Ukraine is threatening to sue Russia if it does not agree to write off part of its debt.
Ukrainian Prime Minister Arseniy Yatsenyuk said that all Ukrainian bondholders had agreed on the restructuring deal at a meeting in London on October 14, but a Russian representative did not show up.
He said Kyiv would give Moscow two weeks, until October 29, to agree to likewise trim a $3 billion loan Russia gave Ukraine in 2013.
Yatsenyuk said Kyiv would sue Moscow if it does not agree, though it's unclear what legal basis Ukraine would have.
Moscow has insisted on being fully repaid for the loan, which is due by the end of the year.
Kremlin spokesman Dmitry Peskov said on October 15 that Russia has no intention to agree to any restructuring.
Analysts say Ukraine's potential failure to pay up in time could mean a showdown between the two countries at the end of December, spilling into possible asset seizures.