Ukraine's acting interior minister has alleged that the killing of protesters in Kyiv took place under the orders of ousted president Viktor Yanukovych.
The government also announced Thursday the detention of 12 members of an elite riot police unit on suspicion of shooting protesters. More than 100 people were killed during unrest in Kyiv in February.
Meanwhile, Russian Foreign Minister Sergei Lavrov says troops near the Ukrainian border will return to their permanent bases as soon as they finish military exercises.
Ukrainian officials have said as many as 100,000 Russian soldiers along its eastern and southern borders are poised to invade.
NATO's top commander, General Philip Breedlove, said Wednesday the Russian force is "ready to go" and could take over large parts of Ukraine in a little as three days.
Lavrov Thursday called on the West and Ukraine to de-escalate the rhetoric, which he says is becoming unreasonable.
He is also asking NATO for answers on its plans to beef up defenses in Eastern Europe -- a direct response to the Russian takeover of Ukraine's Crimean peninsula.
NATO foreign ministers also announced they will officially end all civilian and military cooperation with Russia. The ministers say they do not recognize the annexation of Crimea and urged Moscow to immediately comply with international law.
Moscow accuses NATO of reverting to Cold War rhetoric.
Mr. Yanukovych, who fled Kyiv in February after months of anti-government protests, said Wednesday he was "wrong" to invite Russian troops into Ukraine's Crimean peninsula.
In his first interview since he sought refuge in Russia, Mr. Yanukovych told the Associated Press and Russian NTV television that he will try to persuade Moscow to return the territory to Ukrainian control.