Russia says the price of gas for Ukraine could more than double next year.
Another round of talks is being held in Moscow between Gazprom and Ukrainian energy executives in an attempt to reach a deal that would allow Kiev to receive gas after 1 January and guarantee smooth transit of supplies to Europe.
The dispute over debts and prices is the fourth in four years.
Gazprom said on Monday there was a 50% chance of a cut in supplies from 1 January if Ukraine fails to pay its debts.
It also said the gas price for the next year may be much higher than the $US179.5 per 1000 cubic metres that Kiev currently pays.
Europe receives a quarter of its gas from Russia, most of which is transported across Ukraine. A supply cut in January 2006 after a similar row between Kiev and Moscow briefly affected European consumers.
Ukraine currently owes more than $US2 billion, according to Gazprom.
The company has said it will sign an agreement for next year only after Ukraine fully pays the debt.
