Kiev said it had arrested suspects who had been armed and instructed in Russia in connection with a blast that killed at least two people Sunday in a crowd at a pro-Ukrainian rally far from eastern Ukraine's war zone.
Ukrainian authorities fear violence could spread from two rebellious provinces to other areas in the mainly Russian-speaking east, a swathof territory the Kremlin calls "New Russia."
The bomb in Kharkiv, the biggest city in the east, struck one of numerous events across Ukraine on Sunday marking the deaths of 100 protesters a year ago in an uprising that toppled a Moscow-backed president.