Kiev has blamed its former president Viktor Yanukovich and Russian security services for the use of deadly force against protesters in February, as Moscow threatened to cut gas supplies to Ukraine unless it accepted sharply higher prices and paid outstanding bills.
Relations between the neighbours continued to deteriorate yesterday, amid a flurry of accusations that saw Moscow claim to have foiled terror attacks by Ukrainians, and Kiev announce that two Russians had been prevented from abducting a candidate in May’s presidential election.
More than 100 protesters died in increasingly violent protests against Mr Yanukovich’s rule, which culminated in scores of people being shot dead in central Kiev on February 18th and 20th. The president and his entourage fled on February 21st and a new pro- EU government took power.
"What was planned under the guise of an anti-terrorist operation, but which was actually an operation of mass killing, took place under the immediate and direct leadership of former president Yanukovich," said Valentyn Nalyvaichenko, the head of the Ukrainian Security Service (SBU).
After coming under growing public pressure to show results of their investigation, prosecutors announced that 12 members of the Berkut riot police had been arrested, and said their so-called "Black Squadron" and a special SBU unit had been involved in the shootings.
From exile in Russia, Mr Yanukovich has denied ordering the security services to open fire, and critics of the new government have accused their supporters – who include nationalist revolutionary groups – of being behind the shootings.
About 17 police officers were also killed in Kiev, many from gunshot wounds. A few protesters were seen carrying pistols and hunting rifles, but there is a lot of footage showing men in security service uniform firing rifles and automatic weapons towards demonstrators.
Mr Nalyvaichenko also said members of Russia's Federal Security Service (FSB) were in Kiev during the protests, that Ukrainian security officials had kept in close contact with them, and that Russian aircraft had flown explosives and weapons into Kiev airports.
"We have serious reason to believe that these groups, who were at an SBU base, took part in the planning and implementation of this so-called anti-terrorist operation," said Mr Nalyvaichenko, who asked Moscow to clarify the identity of the FSB officers and what they did while in Ukraine.
An unnamed representative of the FSB denied the allegation, telling Russia’s Ria news agency: “Let these statements be on the conscience of the Ukrainian Security Service.”
The FSB said last night that 25 Ukrainians had been arrested while planning "terrorist attacks" in seven Russian regions in mid-March. It said some were members of Right Sector, a Ukrainian nationalist group that came to prominence during the Kiev protests.
Right Sector rejected the claim as “Kremlin propaganda against Right Sector and against independent Ukraine”.
Ukraine’s SBU made further allegations last night, saying two Russian citizens had been detained in western Ukraine while carrying bullets and what appeared to be material for making an explosive device. They are suspected of planning to kidnap several people, including a candidate in May 25th presidential elections. The SBU did not name the candidate.
Russia yesterday sharply raised the price of gas exports to Ukraine for a second time this week.