Gazprom has reaffirmed its Monday deadline for Ukraine to pay its debts after talks between Moscow and Kiev ended without agreement.
The Russian gas giant said it will cut Ukraine’s supply if Kiev fails to pay $1.95bn (£1.15bn) by 06:00 GMT.
“We reached no agreement. The chances that we meet again are slim,” Gazprom spokesman Sergei Kuprianov said.
Ukraine’s discounted rate for gas was axed in April after Moscow accused Kiev of failing to pays its bills.
Mr Kuprianov said Russia would switch to a pre-payment system if it did not receive the money, meaning Moscow could cut off gas supplies to Ukraine.
Correspondents say the European Union could be affected if Gazprom cuts its supply to Ukraine.
Earlier this month, Gazprom gave Ukraine more time to settle its gas bill after receiving a part-payment of $786m (£469m).
Ukraine said it refused to clear its debts completely in protest at Gazprom’s recent 80% price increase.
Gazprom ended its discount price for Ukraine, which was negotiated by former President Viktor Yanukovych last December, in April.
Before the discount was cancelled, Ukraine’s gas bill was heavily reduced by Russia to $268 per 1,000 cubic metres.
The price is now $485.50 per 1,000 cubic metres, the highest in Europe.
Almost 15% of gas used in Europe comes from Russia via Ukraine, which is why EU members are taking a particularly close interest in the stand-off, observers say.
The talks that ended on Monday had been brokered by EU representatives. BBC
