Innocent European monitors

Don't get me wrong. I fully trust US and European governments and their declarations and claims.  I know that those governments would never lie and would never ever engage in espionage in other countries. That just does not happen. Only Russia spies.  But may I ask you about those monitors? What are they doing there and what is their mission exactly? What are they monitoring?  "The detained men are military officers who also were here under OSCE auspices, but under a separate mission from the civilian observers....It was not clear why the monitors, who were in military uniform but unarmed, decided to try to enter Slovyansk on Friday. The city, which has been known for weeks as a hotbed of separatist sentiment, was especially tense after a deadly Ukrainian military assault on several separatist checkpoints just a day earlier. "