Acting Interior Minister Arsen Avakov also accused his predecessor of employing gangs of killers, kidnappers and thugs to terrorize and undermine the opposition during Ukraine's tumultuous winter of discontent.
The preliminary findings revealed by Kiev's new leadership examined the months of anti-government protests that culminated in the deaths in February over 100 people in Kiev, mostly protesters. That violence forced a truce between the opposition and the government, but that arrangement quickly collapsed, and President Viktor Yanukovych fled to Russia.
In the weeks since the bloodshed, Russia seized and then formally annexed Crimea, Ukraine's strategic Black Sea peninsula, and the U.S. and the European Union slapped sanctions on those responsible, mainly Russian President Vladimir Putin's inner circle.
Also Thursday, Ukraine sent 16 senior officers to Bulgaria to join a NATO military exercise in a very public demonstration of cooperation between the alliance and the crisis-torn former Soviet republic. The drills involved over 700 troops from 13 NATO member and partner nations and were being held just a few hundred miles away from Crimea.
Speaking at a televised press conference in Kiev, Avakov accused Yanukovych's government of ordering snipers to shoot at protesters from rooftops near the city's central square, known as the Maidan. He said 17 people were killed from one location and one government sniper alone killed as many as eight people.
Ukrainian Security Service chief Valentyn Nalyvaichenko charged that Yanukovych himself had ordered the killings.
"What was planned under the guise of an anti-terrorist operation, and which was in fact an operation of mass killing of people, took place under the immediate and direct leadership of former president Yanukovych," Nalyvaichenko said.
He did not elaborate on how he knew this information, whether it was from witnesses, government documents, airline records or other sources.
Prosecutor General Oleh Makhnitsky said 12 members of an elite riot police unit named "Black Squadron" have been detained on suspicion of shooting protesters,
Nalyvaichenko also said there was evidence that Russia's FSB security service assisted its Ukrainian counterparts' attempts to suppress the anti-government protests. He said groups of FSB members were deployed at a Ukrainian security facility — 26 in December and six in January — and that they took part in planning and implementing anti-protest measures. He said the Russians even interrogated the Ukrainian security chief.
Nalyvaichenko contended that in late January, when peaceful protests turned into bloody street clashes with police, Russia sent planes to Kiev carrying massive amounts of explosive devices, arms and crowd control devices "to organize executions and the extermination of our protesters on the Maidan."
Russia's FSB, the successor agency to the KGB, swiftly dismissed the claims, telling the state news agency RIA Novosti that the allegations should "rest on the conscience of the Ukrainian Security Service."
The identity of the snipers believed to be responsible for most of the deaths is the subject of bitter disagreement.
The interim government says Yanukovych ordered snipers to be deployed and to fire at protesters — a charge that Yanukovych denied in an AP interview Wednesday in Russia.
Opponents of Ukraine's current leadership, meanwhile, say some snipers were also organized by opposition leaders trying to whip up outrage.
The new health minister, Oleh Musiy, who previously served as the protesters' top medic, has said he treated both protesters and riot police with similar types of sniper wounds.
The speakers at Thursday's presentation skirted a question on whether any snipers were also shooting at police. Avakov said establishing who was responsible for the deaths of law enforcement officers would be part of the broad investigation that is still ongoing.
Avakov also detailed what he described as overwhelming evidence linking former Interior Minister Vitali Zakharchenko, who was in charge of police during the protests, to a person coordinating hired thugs that perpetrated a campaign of beatings and intimidation against opposition activists.
Avakov said another underworld figure operating under Yanukovych's and Zakharchenko's patronage ran a group of 10 people carrying out beatings and kidnappings of protest organizers, including the kidnapping of a prominent activist and his colleague. The latter was killed in the attack.
In his interview with the AP, Yanukovych said Wednesday that he "was wrong" in inviting Russian troops into Crimea, which was swiftly annexed by Moscow following a referendum in which the vast majority of residents backed a reunion with Russia.
Ukraine's fledging government and Western leaders have since expressed concern about a recent buildup of Russian forces near the Ukrainian border.
U.S. Air Force Gen. Philip M. Breedlove, who commands all NATO forces in Europe, said Russia has 40,000 troops along the border with neighboring Ukraine, and that they are capable of attacking by land and air on 12 hours' notice.
The sheer size and posture of Russia's forces are destabilizing, although the Russians' plans remain unknown to NATO, Breedlove said.
Given their capabilities, the force would be able to push all the way to the Ukrainian port city of Odessa or the breakaway ethnic Russian enclave of Trans-Dniester in Moldova, he said. Alternatively, the Russians could open a "land bridge" through Ukrainian territory to the south, toward Crimea, or just stand pat and exert pressure on Ukraine's May 25 presidential election, he said.
Putin says the troops are there for military exercises. Russian Foreign Minister Sergey Lavrov told reporters Thursday that the Russian troops will be returning to "their permanent quarters as soon as other participants of the exercise have completed their tasks."
Lavrov, however, accused the Ukrainian government "and their patrons in the West of blowing this out of proportion," adding that Russia did not violate any international norms by sending additional troops to its own border.
Yanukovych, in the interview with AP and Russia's state NTV television, did not answer several questions about whether he would support any Russian moves into other areas of Ukraine on the pretext of protecting ethnic Russians.
Peter Leonard in Kiev, Nataliya Vasilyeva in Moscow and John-Thor Dahlburg in Brussels contributed to this story.
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