Gas deliveries to Kiev could be disrupted if Ukraine's Naftogaz does not pay its debts to Russian energy concern Gazprom by Monday morning, June 16.
The money that is to be transferred to the Russian company amounts USD 1.95 B.
Hours before the deadline, a new session of talks that started between Kiev and Moscow over the weekend ended without yielding any results.
Russia did not agree to Ukraine's latest offer, under which it would pay USD 326 per 1000 cubic meters of gas, and insists the price could not go below USD 385.
A spokesman for Gazprom, Sergey Kuprianov, was quoted by Russia's RBC Daily as repeating threats issued by the company that a system of advanced payment would be imposed on Ukraine if it does not send the money it owes.
Such a negative development for Ukraine, which is struggling with the economic and financial impacts of its recent political crisis, could also put supplies to Europe in jeopardy.
The pricing dispute started after Russia announced a 80% price hike for the gas delivered to Ukraine in April.
Ukraine currently has to pay USD 485.5 per 1000 cubic meters, but rejects that price.