Until now, there have been no reliable reports about potential regular Russian troops ('little green men') operating inside Ukraine.
It's also a first that there is solid evidence for insurgents creating new fronts
far away from their frontline positions, presumably by attacking from Russia (in fact, it might be the first time I've seen that kind of claim, reliable or not - all the previous claims about attacks from Russia happened near existing rebel frontlines).
All in all, a significant escalation as it means that a lot of the previous plausible deniability disappears with this apparent shift in strategy.