A Reuters TV witness said he had seen two bodies, one with gunshot wounds to the head and face, at a checkpoint outside the city of Slaviansk in eastern Ukraine where separatists said earlier they had come under armed attack.
One of the dead was dressed in combat fatigues and the other in civilian clothes. Police were at the scene carrying out an investigation, he said.
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.