Interesting situation going on in Ukraine.
The video in this link shows the method of operations by the Russians:
http://fotografmariasoderberg.blogspot.se/2014/04/12-april-2014-uppror-i-kramatorsk-utan.html
Some of the dialogue is translated to Swedish. It's basicly pointing out the lack of willingness to engage in dialogue by the armed men when the police chief tries to talk to them.
Anyway the interesting part is how effectively and professionally they secure the building. I'm not sure if they are shooting at something or just in the air, I'm assuming in the air to scare away the unarmed cops and civilians. Probably had enough of all the chatter.
Then there is some shooting into the building. Probably to scare anyone inside and to avert any ambush. Then they appear to set up to clear the building. The video looks like it was cut at this point, and from their stances they appear to be covering the inside and an ingress area now. Cue what I assume is an unhappy local being ushered a ay with a man in civilian clothing with a pistol. Another cut(at 3:32), and now it looks like the extras are coming, after the area has been secured. Some guy tries to kick after them(hmm). Quickly the extras are in sufficient number to constitute a crowd, and now the cameras can show a fall of Bagdad moment. No statue here so it's the Ukrainian flags that are being removed. This is much lower budget than the US version of course.
Notice the soldiers protecting the men and keeping the public away. One could get the idea they aren't welcome.

Looks like another cut at 4:26. Some shooting happens and it seems everyone joins in with covering fire. As the camera person takes cover I hear a sound which could potentially be from a Machine Gun(PKM could be assumed).
So we got a combat Unit escorting the extras for what looks like a camera op for a "protester" takeover.
So who are the Armed men?
Looking at the pic in this thread of them, they are armed with Russian issue AK-74m's. Don't think Ukraine has moved beyond the ak-74, and they are likely not from the local police. They would have older hand me downs like aks-74U's or perhaps standard issue ak-74s or aks-74's.
So they are likely from Russian official sources. My guess is that they are organized and trained by the GRU/SVR, with perhaps some operatives among them. Standard fifth column operation.
The Russians could have made it more convincing by perhaps making them look a bit more ragtag, but for their purposes they don't have to be more convincing. They are only needed to fool Russian TV viewers. And they obviously trust their media and think it's alright to be fooled in the public interest:
http://www.tol.org/client/article/24244-lie-to-me.html
So those who watch Russian media will likely have a view of reality that is foreign to most people, and will often view the non Russian press as western propaganda. Thats why it's a bit risky for non Russian journalists in some areas of eastern Ukraine.
What worries me is that these kinds of operations are supposed to be started as a prelude to invasion or something. In Crimea, these units were the men who took over official buildings before the regular Russian troops arrived to reinforce them.
It could be Putin is waiting for some kind of excuse to go in. Perhaps hoping for the Ukrainians to go all in so he can sell it to the Russian public that they are intervening to stop a civil war or something. The 12x flyover of the US Destroyer could seem like some kind of provocation. But apparently the Ship could tell the Fencer was unarmed. Had they not known that plane would have been shot down.
Interestingly It seems that the majority of these building takeovers etc. are happening in Donetsk Oblast. That's were Janukovitsj is from, and apparently all of the ministers in his government IIRC.
Ps.: Seems like Lukashenko(Belarus) recognizes Turchynov(acting president) as legitimate leader of Ukraine. Very interesting that he is not towing Putins line on this.