"The conflict is moving from a political one to a military one because of Russian soldiers," he told a meeting at Ukraine's defence ministry. "Today, Russian soldiers began shooting at Ukrainian servicemen and this is a war crime without any expiry under a statute of limitations."
Yatseniuk said he had ordered Ukraine's defence minister to call a meeting with his counterparts from Britain, France, and Russia - signatories to a 1994 treaty guaranteeing Ukraine's borders to "prevent an escalation of the conflict".
Earlier, a military spokesman said a Ukrainian officer was wounded in a shooting at a military facility on the outskirts of the Crimean capital Simferopol, but it was unclear who was behind the incident.