[anc84]

Are there any reputable sources or archives for this claim?

[korisnik]

Yes. Many news sources reported on it.

As for the actual content in question - here's an archive of a tweet of them boasting about having Buk missile launcher, the tweet was later deleted:

http://web.archive.org/web/20140707150151/https://twitter.co...

Here's a screenshot of the VK account where their (now former) commander and defense minister (and allegedly "ex" FSB member) claimed the downing of a Ukrainian plane, later the content was deleted:

http://i.imgur.com/fi4Zkx6.png

The Wikipedia article covers all that in depth:

https://en.wikipedia.org/wiki/Malaysia_Airlines_Flight_17

[kbart]

http://www.dailymail.co.uk/news/article-2696389/That-blast-l...

http://www.interpretermag.com/was-col-strelkovs-dispatch-abo...

..and many others

[07d046]

There's this tweet by a rebel commander: "Message from the militia. / / In the area Torrez just downed aircraft, like the An-26"

From http://blog.storyful.com/2014/07/19/how-social-sleuthing-unc...

[tptacek]

Anne Applebaum is a very credible, very reputable journalist covering the region:

https://twitter.com/anneapplebaum/status/489806406833680384