The killings of Ukrainian protesters during February's anti-government demonstrations took place "under the direct leadership" of ousted President Viktor Yanukovich, security chiefs have said.
The charges were made on Thursday by the prosecutor general and heads of the Interior Ministry and state security. They blamed the deaths of at least 100 demonstrators, many of whom were killed by police snipers, on the disbanded Berkut riot police.
Acting Interior Minister Arsen Avakov said Yanukovich issued the "criminal order" to fire at the protesters, while agents from Russia's Federal Security Service (FSB) helped him to plan and carry out the deadly assault between February 18 and 20.
"FSB agents took part in both the planning and execution of the so-called anti-terrorist operation," he said.
At least 12 members of the disbanded Berkut unit have been detained on suspicion of "mass murder".
Acting Prosecutor General Oleh Makhnitsky said that those detained included the head of a specialised company, which he called the "Black unit", which operated within the Berkut riot police. The unit had allegedly handed out weapons for use against demonstrators.
"The police officers of this company were trained for special operations including the killing of people. They were overseen by the presidential administration," Interfax Ukraine news agency quoted Makhnitsky as saying.
However, the identity of the snipers has been disputed.
Russia dismisses allegations
Sergei Lavrov, the foreign minister of Russia, where Yanukovich sought asylum after being forced out of power by mass protests, said Ukrainian officials' claims were not credible, according to the Associated Press news agency.
"Truth should be established transparently and in full scope," Lavrov said on Thursday. "I don't want to judge now how precise and reasonable the announcement [by the Ukrainian authorities] is. Anyway, it contradicts a massive amount of evidence to the contrary."
He was speaking following a meeting of foreign ministers from members of the Collective Security Treaty Organisation (CSTO)
The CSTO is a regional military alliance comprising Russia and five other post-Soviet states - Armenia, Kazakhstan, Kyrgyzstan, Tajikistan and Uzbekistan.
Lavrov held talks with fellow CSTO foreign ministers in Moscow.
He said the alliance was not seeking seeking a confrontation with NATO.
"The CSTO is not interested in escalating tensions with anyone including NATO," he said.
Al Jazeera's Kim Vinnell, reporting from Kiev, said officials in Moscow believed far-right ultra-nationalists - rather than government forces - were responsible for carrying out the attacks on protesters, with the end goal of ousting Yanukovich.
In late February, the Interior Ministry disbanded the Berkut, whose name means "Golden Eagle" and signifies a predator capable of swooping quickly onto its prey.
Members of the Berkut police, former paratroopers and marines intended to fight organised crime in the country, kneeled in front of a crowd in Lyiv on February 24, apologising for their use of force during the anti-government protests.
Source: Al Jazeera and agencies