Ukraine's Right Sector nationalists denied playing any role in a gunfight in Slaviansk, eastern Ukraine, in which at least two people were killed. They claimed Russian special forces for being behind the attack.
"It is a blasphemous provocation from Russia: blasphemous because it took place on a holy night for Christians, on Easter night. This was clearly carried out by Russian special forces," Artem Skoropadsky, a spokesman for Right Sector, told Reuters.
Tensions remain high in eastern Ukraine after at least three died in a day of shooting during what was supposed to be an Easter truce.
In an exclusive interview with NBC News, the Ukrainian Prime Minister warns of the dangers of unchecked Russian expansion and aggression.
Russia, the US and the EU say that all sides have agreed to steps to "de-escalate" the crisis in Ukraine at talks in Geneva.