Ukraine will make a prepayment for 1 billion cubic metres of Russian gas on Wednesday or Thursday, Ukrainian Energy Minister Volodymyr Demchyshyn said, as the deepening winter forces the country to rely for energy on its powerful neighbour.

Russia, which cut off supplies to Ukraine in June because of a standoff over prices, has insisted that Ukraine pay for supplies in advance. So far, Kiev has not committed to new orders as a separatist conflict weighs on its flagging economy.

However, increasingly cold weather is forcing the country to turn to Russia as it draws down its severely depleted reserves.

"The prepayment will take place today or tomorrow, I hope today ... We've started drawing on reserves more aggressively," Demchyshyn said at a briefing.

Since the start of the heating season in late October, reserves have fallen 17 percent to 13.9 billion cubic metres as of Dec. 1, according to data from Ukrtransgaz, the state-run gas transport monopoly.

State energy firm Naftogaz declined to comment when it planned to send the payment.