Russia's Gazprom said Monday it switched Ukrainian gas company Naftogaz over to the new payment scheme because of $4.45 billion in overdue bills.

"Payments [for June] also were not received," the company said in a statement. "Starting from today [Monday] the Ukrainian company will receive only prepaid volumes of Russian gas."

Trilateral talks between Russian, European and Ukrainian officials dragged on for most of last week without a breakthrough.

Russia offered some concessions to the Ukrainian side, though the government in Kiev said it was wary of the Russian intentions. European officials have said the region's energy sector was subject to "political and commercial blackmail."

Russia supplies about a quarter of the European Union's gas needs, though most of those supplies run through the Soviet-era transit network in Ukraine. Debt disputes in 2006 and 2009 prompted Gazprom to cut gas to Ukraine briefly, causing regional energy shortages.

Alexei Pushkov, the head of the Foreign Affairs Committee in the state Duma, said Monday the switch to a pre-payment scheme was long overdue.

"Let [Ukrainian Prime Minister Arseniy] Yatsenyuk get shale gas from the United States," he said.