Kiev - EU foreign ministers prepared to meet over the Crimea crisis in Athens on Friday after Ukraine's Western-backed leaders blamed Russian agents and the country's ousted president for organising the bloodshed during February protests that claimed nearly 90 lives.
The explosive allegations were levelled only moments before Russia responded to the new course taken by the ex-Soviet neighbour by hiking the price it must pay for gas shipments to what Ukrainian officials say is the highest rate for any European state.
Washington reacted by warning Russia that "a country should not use supply and pricing terms as tools of coercion to interfere in Ukraine or elsewhere," said White House spokesperson Jay Carney.
Moscow also lashed out at its old Cold War nemesis Nato for building up the defences of ex-Communist and former Soviet republics that have felt threatened by Russia's recent annexation of Crimea and massive build-up of forces near Ukraine.
The fierce East-West fight for Ukraine's future has exposed the deep divide that splits the nation of 46 million between those who see themselves either as culturally tied to Russia or as part of a broader Europe.
Those tensions exploded on 18 February when gunshots in the heart of snow-swept Kiev heralded the onset of pitched battles between riot police and protesters - some armed with nothing more than metal shields - that left scores dead.
Both sides have blamed the other for starting the violence, but there had been no formal probe results unveiled until acting interior minister Arsen Avakov presented his initial findings to reporters on Thursday.
Avakov's conclusion was decisive and potentially devastating for the new leaders' relations with Russian President Vladimir Putin.
He 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," Ukrainian Security Service head Valentyn Nalyvaichenko told the same press briefing.
An FSB spokesperson told Russia's state-run RIA Novosti news agency that Ukraine's allegations were patently false. Russian Foreign Minister Sergei Lavrov for his part said "huge amounts of evidence" contradicted Kiev's claims.
Yanukovych fled to Russia only days after the carnage and is now wanted in Kiev for allegedly ordering police to open fire against the crowds - a charge he denies but that is likely to keep him out of Ukraine for years to come.
"Former president Yanukovych will be prosecuted," Ukrainian Prime Minister Arseniy Yatsenyuk told the BBC. "He is accused of mass murder and we will bring him to justice."
Meeting under Greece's six-month EU presidency in Athens, European Union foreign ministers will discuss the Crimea and Ukraine crisis from 0930 GMT on Friday.
Russia ups Ukraine payments
Russia's NTV channel reported that security services had detained 25 Ukrainians suspected of planning "sabotage" and "terrorist attacks" between 14 March and 16 March in seven Russian regions.
It said the group contained three activists from Pravy Sektor, a radical nationalist group in Ukraine, and claimed all 25 were following "instructions" from the Ukrainian security agency, the SBU.
NTV aired a brief video of the detainees being questioned. It showed three young men speaking to the camera. The newsreader's voiceover drowned out their testimonies.
Earlier on Thursday the SBU said it had detained two Russians in the western Lviv region who had planned to take Ukrainian politicians hostage, including a presidential candidate.
NTV is owned by a bank affiliated to state-owned gas giant Gazprom. It is known for showing smear documentaries that target critics of the Kremlin.
US President Barack Obama briefed top congressional leaders on his consultations with world leaders in Europe last week seeking support for his strategy to isolate Russia and back Ukraine.
The raging security crisis on the eastern edge of the European Union has been accompanied by months of economic pressure that Russia had poured on Ukraine in a seeming effort to force its leaders to reverse their Westward course.
Gazprom - long accused of being wielded by the Kremlin as a weapon against unco-operative neighbours - on Tuesday hiked the price it charges Ukraine for natural gas shipments, on which its industries depend, by 44%.
The punitive but largely expected step eliminated a price discount that Putin had extended to the old government in December in reward for its decision to reject closer EU ties.
But Ukraine saw the price it must pay for 1 000 cubic metres of gas jump by another $100 to $485.50 following a failed round of negotiations in Moscow with the chief executive of Russia's state energy firm Gazprom.
Moscow argues that a $100 rebate it awarded Kiev in 2010 in return for its decision to extend a lease under which the Kremlin keeps its Black Sea Fleet in Crimea no longer applied because the peninsula was now a part of Russia.
Kiev has vowed to contest the new charge - a warning that threatens a repeat of the 2006 and 2009 halts in gas supplies to Ukraine that also affected many of Russia's other European clients.
Nato defends security boost
Europe's worst security crisis in decades appeared to be only gaining momentum after Nato boosted the air power of Eastern European nations that Putin still views as part of Russia's strategic domain.
Nato chief Anders Fogh Rasmussen on Thursday defended that move against Russian claims it violated international law.
"I'm actually surprised that Russia can claim that Nato has violated its commitments because Russia is violating every principle and international commitment it has made," Rasmussen said.
"First and foremost the commitment not to invade other countries," he added.
The 28-nation alliance has said firmly it did not intend to get militarily involved in Ukraine no matter what Russia did.
The US Air Force this week sent 10 F-15 fighters to help Nato expand its military presence in the three tiny ex-Soviet Baltic nations.