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An Ukrainian soldier stands guard at a checkpoint of Pletnyovka, Kharkiv region on Ukraine-Russia border, where Russian humanitarian convoy is due to cross the border on August 13, 2014.

The International Monetary fund agreed to a $17 billion bailout program for Ukraine in April, but the fund warned earlier this month the country could need as much as $19 billion in additional international financing if fighting continued in the eastern part of Ukraine.

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Dollar denominated Ukrainian bond yields have also climbed to unsustainable levels, with yields on 2023 paper exceeding 10 percent.

Gontareva said the IMF program had already factored in the country's bond liabilities, so no restructuring is necessary.

But head of global macro investor relations at Oxford Economics, Gabriel Sterne said Ukraine's debt levels currently looked unsustainable, predicting a default for November 2015.

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Ukraine's shorter-dated maturities are more likely to be paid out, but holders of longer-dated maturities are at risk of a haircut, Sterne said.

"Greece's default was triggered by a too-big-to-pay bond. The date was shortly before the 12 billion euro ($15.5 billion) maturity in March 2012. We think Ukraine's mostly likely default date is November 2015, shortly before the Russian-held bond matures on 20 December," he said.

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Ukraine shrugs off fears of Greek-style default