Arsen Avakov, Ukraine's interim interior minister, said his predecessor Vitali Zakharchenko, currently on the run, was directly involved in giving orders to shoot at protesters, along with the SBU security services.
Valentyn Nalivaichenko, the new head of the SBU, added that a number of officers from Russia's FSB had been consulting with the SBU in Kiev in December and January, and that Russian citizens were present at SBU headquarters.
He also claimed that explosives and weapons were delivered to Ukraine from Russia during the protest period.
More than 100 people were killed during February's violence.
The ousted president, Viktor Yanukovych, denied he had any involvement in ordering the sniper attacks during an interview on Thursday.
Yanukovych fled Kiev shortly after the shootings and eventually left Ukraine for Russia, where he now lives.
He still claims to be the legitimate president of Ukraine, although even his own party has disowned him.
He confirmed on Wednesday that he had asked Russia to send troops to Crimea, a decision he now says was a mistake, after Moscow moved to annex the territory last month.
The Kremlin has put forward a different version of events, alleging the violence that spurred Yanukovych's downfall was organised by far-right radical protest groups keen to radicalise the situation.
On Sunday, Russia's foreign minister, Sergei Lavrov, said Moscow had evidence that Ukrainian nationalist groups were behind the sniper attacks.
In an interview with the Russian media, he said that while he could not be 100% certain, "many factors point to this".
Lavrov said he had repeatedly raised the allegations with western partners and hoped they would not be swept under the carpet.
There is also footage that purportedly shows snipers shooting at protesters and riot police, which Russia says is evidence that the violence was carried out by "provocateurs".
A recording of a phone call between the EU foreign affairs chief, Catherine Ashton, and Estonia's foreign minister, Urmas Paet, was leaked last month – with suspicions falling on Russian intelligence or organisations close to it – in which the pair discussed the theory that the opposition itself was responsible for the snipers.
Paet tells Ashton he has heard discussions in Kiev in which people claim possible involvement, to which Ashton responds with surprise.
Russian media have seized on the call as evidence that there has been a western cover-up about supposed involvement.
On Thursday, Ukrainian officials said their investigation had determined some, but not all, of the sniper locations, and that 12 people had been arrested after thousands of riot police were questioned.
Officials said some of the Berkut (special police) officers whom Kiev wants to arrest were in Crimea.
Hundreds of Berkut returned to the peninsula after the violence in Kiev and were treated as heroes.
After the new government disbanded the regiment, Russia said it would give Berkut officers passports and integrate them into Russian security services, while former Berkut officers played a part in the Crimean "self-defence" forces that sprang up before the Russian moves to annex the territory.
Source: The Guardian