from The Guardian
I have little doubt that Russian security services were in some way involved in the recent escalation of violence in several towns in eastern Ukraine.
The seizures of administrative buildings on 12 April were well co-ordinated between different towns, the armed men were well equipped and showed high levels of military training. This does not necessarily mean that Russian special operations units are directly taking part; those men could be former Ukrainian riot police officers, many of whom fled to Crimea and Russia to escape punishment from the new government.