No I doubt it that these are militias, they're behavior in holding security (360 degrees) and glancing back and being aware of their buddies in their units seems too professionally done. Even at a take over or revolt in certain specific government buildings in eastern Ukraine speaks volume about the strategy and the importance of that particular place due to importance of strategical advantage any army would try to do during a war or conflict. It't not the government building that's importance but rather the terrain, highways, river ways, check points, communications, and data gathering that's behind it that's important. Yes IMO these are FO (forward observers) disguise as militias going on a recon mission.
I think there is little doubt that many of these guys are trained and may be serving or recently serving personnel. Jura,s link and the mainstream media of both sides fully accept that the armed protesters are a mix of ordinary citizens, and defected military/police units. There are plenty of pictures of former Birkat forces, still in uniform, joining the forces inside the Donetsk government buildings. It is also no coincidence that many of the facilities stormed earlier this week held significant arsenals of automatic weapons and ammunition.
I am however pretty confident that we are not seeing the deployment of regular units of the Russian Federation.
I do suspect that many people underestimate the level of organisation that the rebels have. They seem to be run by representatives from civil government, local security forces and the Industrial Trade Unions and other civil groups. While I am also sure that critical elements of support and intelligence are coming from Russia, most of the running is being done by the locals themselves.
The revolt certainly seems in full steam and spreading across an ever wider area of the Russian speaking parts with news of new clashes and occupations in Kharkov.
It is however pretty clear that this is not the automatic prelude to a Russian invasion but rapid changing of the facts on the ground prior to the talks in Geneva scheduled for Thursday.
Lavrov seems to be making no secret of it.
"Try and stop what is happening and we will cancel" That is pretty hardball and the clear inference, that it is in the interest of Kiev and their backers to start talks sooner, rather than later, or risk losing any real leverage for talks as the revolt passes tipping point and threatens to engulf the whole Ukraine and not just the East.