Here we go...

SLOVYANSK, Ukraine — Ukrainian special forces moved in Sunday to confront a separatist revolt in eastern Ukraine, engaging in gunfights with armed pro-Russian militants who had stormed a Ukrainian police station here. At least one officer died in the operation and several others were injured, along with four local residents, Ukrainian officials said.

The police station was one of several security centers in the eastern region of Donetsk seized on Saturday by unidentified masked gunmen in a series of coordinated raids that Ukrainian authorities denounced as Russian “aggression.”

This is the sort of thing that Putin or anyone else trying to make a move on contested territory will be prepared to take full advantage of.   The next few days will tell, but unless there is some serious moves to get NATO troops into Ukraine to counter the nearby Russian forces, it looks like the latter will go for it.  "Special forces" in this case means that numbers are still small and the Speznatz greatly outnumber anything the Ukraine can put in the field, so tit-for-tat fights like this will quickly swing Russia's way.

NATO commanders have been trying to get the politicians to take things seriously, but so far only the Poles are doing so, and they mostly in their own legitimate self-interest.  Were I the Ukraine right now, I'd mobilize everything on a full war/tactical footing and get dug in as advantageously as possible.  A stand up fight is the one thing the Russians don't want, as it destroys any semblance of "will of the people".  Watch and (hopefully don't) shoot.