Ukraine's new Western-backed leaders on Thursday blamed Russian agents and the ousted pro-Kremlin president for organizing two days of carnage in Kiev that killed nearly 90 supporters of closer EU ties.

The explosive allegations were leveled only moments before Russia responded to the new course taken by its ex-Soviet neighbor by hiking the price it must pay for gas shipments on which its industries depend to what Ukrainian officials say is the highest rate for any European state.

The furious battle for Ukraine's future between Moscow and the West has exposed the deep divide that splits the nation of 46 million between those who see themselves as either culturally tied to Russia or a part of a broader Europe.

Those tensions exploded on February 18 when gunshots in the heart of snow-swept Kiev heralded the onset of pitched battles between riot police and protesters that left scores dead.

Both sides have blamed the other for starting the violence. But no formal probe results had been unveiled in Kiev until acting Interior Minister Arsen Avakov presented his initial findings to reporters on Thursday.

Avakov said that deposed president Viktor Yanukovych had issued the "criminal order" to fire at the protesters while agents from Russia's Federal Security Service (FSB) helped him plan and carry out the assault.

"FSB agents took part in both the planning and execution of the so-called anti-terrorist operation," Avakov said.

An FSB spokesman told Russia's state-run RIA Novosti news agency that Ukraine's allegations were patently false.

"Let those allegations remain on the conscience of the Ukrainian security service," the unnamed FSB official said.

Also on Thursday Russia increased the gas price for Ukraine to $485 per 1,000 cubic meters and urged Kiev to pay its $2.2 billion debt, stepping up pressure on an economy already on the brink of bankruptcy.

The head of Russia's top natural gas producer, Gazprom, told Prime Minister Dmitry Medvedev that from this month the price would rise by 26 percent after Moscow introduced an export duty on gas to Ukraine.

Meanwhile, Russian Foreign Minister Sergei Lavrov said Thursday Russia wanted answers from NATO regarding its activities in Eastern Europe after the  military alliance promised to beef up defenses for its eastern members.

"We have addressed questions to the North Atlantic military alliance. We are not only expecting answers, but answers that will be based fully on respect for the rules we agreed on," Lavrov told reporters at a briefing with his Kazakh counterpart.

NATO foreign ministers at a meeting this week ordered military commanders to draw up plans for reinforcing NATO's defenses.

Military planners will come back with detailed proposals within weeks, a NATO official said.