"We’re continuing to support our largest importer - Naftogaz Ukrainy," Gontareva said.

"Last month, the volumes of currency sales to Naftogaz directly from reserves amounted to $500 million," she said.

Naftogaz mainly buys Russian gas from abroad, but in recent months the Ukrainian government has been attempting to diversify its supply sources, importing small but growing quantities of gas from Slovakia, Hungary and Poland.

Ukrainian President Petro Poroshenko recently said Ukraine intends to give up buying Russian gas completely within the next two years.