Ukrainian security officials say the killings of protesters in Kyiv in February occurred "under the direct leadership" of ousted President Viktor Yanukovych, and accused Russian security services of involvement in the repression.
Interior Minister Arsen Avakov told a news conference in Kyiv on April 3 that Yanukovych "issued the criminal order...to open fire against protesters on February 18-20."
More than 100 people were killed during the protests which started in November, most of them between February 18 and February 20. Many of those who died appeared to have been killed by snipers.
Yanukovych fled the day after the worst of the killings by sniper fire on February 20 and was later ousted by parliament.
In Moscow, Russian Foreign Minister Sergei Lavrov said that "huge amounts of evidence" contradicted the statement by Ukrainian authorities that snipers loyal to Yanukovych opened fire on Kyiv protesters.
Lavrov told reporters that "the truth about snipers has to be established in a transparent way."
Russia has previously suggested that Ukrainian ultranationalists were the first to open fire against the police, in an effort to spark a larger altercation that could then be blamed on Yanukovych and his backers in the Kremlin.
SBU: Russian Involvement
Valentyn Nalyvaychenko, the head of the Ukrainian Security Service (SBU), said at the same news conference that employees of Russia's Federal Security Service (FSB) were present in Ukraine during the antigovernment protests on Kyiv's Independence Square.
"The first question -- on December 20, 2013, at the grounds of an SBU polygon, there were 26 staffers from the FSB of the Russian Federation," he said. "We are asking for an explanation about their activities there, their ranks, and assignments."
Nalyvaychenko added that investigators believe that FSB staffers were involved in organizing the shootings.
"In mid-January 2014, there were six [FSB] staffers, citizens of the Russian Federation [at the SBU]," he said. "Again -- what were they doing here, what was their assignment, and what was in the making? We have grounds to believe that the same groups of [Russian citizens] that were based on one of the SBU polygons were involved in the planning and implementation of the so-called antiterrorist operations."
Ukraine's acting Prosecutor-General Oleh Makhnitskyy repeated his earlier statement regarding arrests of the members of Ukraine’s disbanded special police unit, the Berkut, suspected in shooting antigovernment protesters.
"With the use of a number of criminal investigation techniques, including psychological and physiological interrogations with the use of a polygraph we have identified individuals who were directly involved in shooting at people [on Independence Square]," he said. "As of today, 12 members of a specialized squad of the [disbanded] Berkut forces have been arrested and are under investigation."
Meanwhile, Russian FSB officials denied any involvement in the events in question.
"Let those allegations [Nalyvaychenko's statements] remain on the conscience of the Ukrainian Security Service," an FSB spokesman told the RIA Novosti and ITAR-TASS news agencies.
With reporting by AFP, Reuters, RIA Novosti, and ITAR-TASS