Ukrainian officials are blaming Russian agents and the country's ousted pro-Russian president for two days of bloodshed earlier this year at the height of anti-government protests that claimed more than 100 lives. Authorities say many of the dead were killed by sniper fire.
The mystery of the Kyiv protesters' deaths in February has fueled talk of conspiracies. Russian President Vladimir Putin has suggested the demonstrators themselves were the gunmen, acting to discredit the government of then-president Viktor Yanukovych.
On Thursday, acting Interior Minister Arsen Avakov linked special police from its Ministry of Internal Affairs, acting under orders of Mr. Yanukovych, to the killing of at least 17 protesters. He said 12 "Berkut" police have been identified and that authorities have begun arresting them.
For his part, Ukraine's security service chief said evidence shows Russian agents were involved in "the planning and implementation" of the deadly February 18-20 police operations.
The allegations were leveled Thursday in Kyiv, shortly before Moscow announced another huge increase in the price of natural gas that it supplies to energy-dependent Ukraine. The price increase -- the second this week by Russia's state-run energy giant Gazprom -- raises cash-strapped Ukraine's gas costs by nearly 80 percent.
Moscow has twice in the past decade temporarily cut gas supplies to Ukraine -- in the dead of winter on both occasions. In each instance --in 2006 and 2009 -- the cutoffs were spurred by disputes over gas pricing and pipeline fees.
Moscow asserted that it has supplied Ukraine with gas at well below market prices since the dissolution of the Soviet Union in 1991. Settlements were reached in both cases within two weeks of the cutoffs.
This time, however, Russian Prime Minister Dmitri Medvedev has told Gazprom that Ukraine will now pay at a rate equal to other consumer countries. The Kyiv government, which provides about half the country's gas needs with Russian supplies, has condemned the move as politically motivated.
Separately Thursday, Russia said it has detained 25 Ukrainians suspected of preparing attacks in southern and central Russia. Russian media described the detainees as members of ultra-nationalist movements and said the attacks were planned for March 14 through March 17.