Are these from the ‘US Secret Army’ in Ukraine?

Amateur videos have been circulated over the internet alleging that armed forces from the infamous US private security service formerly known as Blackwater roam around in eastern Ukrainian city of Donetsk.
In the footage, unidentified armed men in military outfits equipped with Russian AK assault rifles and American М4А1 carbines are securing the protection of some pro-Kiev activists amidst popular anti-government protests.
The authenticity of videos allegedly made in downtown Donetsk on March 5 is hard to verify.
The protesters in the footage, after several moments of shock, start shouting, “Blackwater!,” and “Mercenaries!,” as well as “Faggots!,” and “Who are you going to shoot at?!” But the armed men drive off in the blink of an eye without saying a word.
Surely these men were not Blackwater – simply because such a company does not exist anymore. It has changed its name twice in recent years and is now called Academi, the Russia Today writes in an article.
At the beginning of the week, Russian state TV reported that several hundred armed men with military-looking bags arrived to the international airport of Kiev.
It was reported that the tough guys are employees of Greystone Limited, a subsidiary of Vehicle Services Company LLC belonging to Blackwater/XE/Academi.
Greystone Limited mercenaries are part of what is called ‘America’s Secret Army,’ providing non-state military support not constrained by any interstate agreements, The Voice of Russia reported.
But they are not the only ones. A Russian national that took part in clashes in Kiev was arrested in Russia’s Bryansk region this week. He made a statement on record that he met a large number of foreigners taking active part in the fighting with police.
He said he saw dozens of military-clad people from Germany, Poland, and Turkey, as well as English speakers who were possibly from the US, Russkaya Gazeta reported earlier this week.