KIEV, Ukraine >> Interim authorities in Ukraine on Thursday accused ousted President Viktor Yanukovych’s government of using a network of hired killers, kidnappers and gangs of thugs to terrorize and undermine the opposition.

A top security official, speaking at the presentation of an official report, said there was evidence Russia’s security service assisted their Ukrainian counterparts’ attempts to suppress anti-government protests which culminated in bloodshed in February that left more than 100 dead.

Also, Prosecutor General Oleh Makhnitsky said 12 members of an elite riot police unit have been detained on suspicion of shooting protesters.

Yanukovych fled the capital, Kiev, after the culmination of the violence that played out over Feb. 18-20, precipitating the fall of his government.

The identity of the snipers believed to be responsible for most of the deaths is subject of bitter disagreement. The interim government says Yanukovych ordered snipers to be deployed — a charge Yanukovych denied in an AP interview on Wednesday.

Opponents of the current leadership say snipers were organized by opposition leaders trying to whip up outrage.

In his interview with the AP, Yanukovych also said he “was wrong” in inviting Russian troops into Crimea, which was swiftly annexed by Moscow following a referendum in which reunion with Russia was backed by 97 percent of those who voted.

Ukraine’s fledging government and Western leaders have since expressed concern about a recent build-up of Russian forces near the Ukrainian border. President Vladimir Putin told German Chancellor Angela Merkel last week that the troops were there for military exercises and that one battalion has already left.

Yanukovych, in the interview with AP and Russia’s state NTV television, did not answer several questions about whether he would support any Russian move into other areas of Ukraine on the pretext of protecting ethnic Russians.

Russian Foreign Minister Sergey Lavrov on Thursday offered further assurances, telling reporters that Russian troops “will be returning to the place of 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 borders.

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 its forces are destabilizing although the Russians’ plans remain unknown to NATO, Breedlove said.

Peter Leonard in Kiev, Nataliya Vasilyeva in Moscow and John-Thor Dahlburg in Brussels contributed to this story.