"Since December Russia's Gazprom has not paid [Ukraine's state oil and gas company] Naftogaz a kopeck for the transit of Russian gas," Ukraine's first deputy prime minister, Oleksandr Turchinov, told local TV on Monday.
Meanwhile, Gazprom spokesman Sergei Kupriyanov told RIA Novosti: "Naftogaz creates the situation itself by not signing the gas transit documents for December and January and for not drawing up the invoices."
"Gazprom cannot pay until the invoices are sent," Kupriyanov added.
The gas standoff between the two countries deepened when Gazprom cut supplies to Ukraine by 25% over the country's unpaid debt Monday.
Ukraine's Naftogaz said, however, that gas had been cut by a further 10% to 35% or 46 million cubic meters. The country receives 135 million cu m of gas a day from Russia.
Russia's energy giant pledged shipments to Europe would not be affected.
In late February, Russia's gas monopoly threatened to cut shipments on March 3 if Ukraine, a major transit country for Russian gas to Europe, failed to pay off its debt and approve a new scheme for future supplies.
"Gazprom is a reliable supplier, but it cannot deliver gas without payment," Kupriyanov said. "The debt for gas supplied to Ukraine has not been repaid as of today. Ukraine is continuing unregulated gas consumption. New contracts have not been signed."
Kupriyanov said around 1.9 billion cu m of gas worth some $600 million had been illegally consumed by the ex-Soviet state.
Ukraine said earlier it had paid over $1 billion to Gazprom to clear its debts for Russian supplies in 2007. Kiev owed Russia a total of $1.5 billion in 2007 and 2008, according to the Russian giant.
Kupriyanov said the monopoly was prepared to continue talks with Ukraine to resolve the dispute.
