I'm wondering, if it is confirmed it is a missile, are there any precedent of civilian plane shot-down like that in modern history (post WWII)?

Edit: Thanks great replies!

There absolutely is precedence for this.

The US shot down an Iranian airliner in 1988: http://en.wikipedia.org/wiki/Iran_Air_Flight_655

And the Russians shot down a Korean airliner in 1983: http://en.wikipedia.org/wiki/Korean_Air_Lines_Flight_007

There are numerous examples, although “like that” is of course a difficult requirement, given that we don’t know what happened yet :)

Some examples (in no particular ordering):

  https://en.wikipedia.org/wiki/Iran_Air_Flight_655
  https://en.wikipedia.org/wiki/Libyan_Arab_Airlines_Flight_114
  https://en.wikipedia.org/wiki/Korean_Air_Lines_Flight_902 (air-to-air, not ground-to-air missile)
  https://en.wikipedia.org/wiki/Air_Rhodesia_Flight_825
  https://en.wikipedia.org/wiki/Air_Rhodesia_Flight_827
  https://en.wikipedia.org/wiki/Korean_Air_Lines_Flight_007 (air-to-air, not ground-to-air missile)
  https://en.wikipedia.org/wiki/1983_TAAG_Angola_Airlines_Boeing_737_crash

Looks like there were quite a few incidents: http://en.wikipedia.org/wiki/List_of_airliner_shootdown_inci...

(The only one I've heard of before was Iran Air Flight 655)

Plenty of them:

http://en.m.wikipedia.org/wiki/List_of_airliner_shootdown_in...

La Strage di Ustica ("Ustica Massacre"): http://en.wikipedia.org/wiki/Aerolinee_Itavia_Flight_870

After more than 30 years we still don't know for sure what happened...

Well, we actually do, really. The French government refused for 30 years to have their pilots interviewed about the issue, relenting only very recently. They even deployed a cover operation to take charge of recovering the relic and mislead investigators. NATO actively impeded investigation at various points, quoting secrecy rules etc etc. The Italian military miraculously "failed" to keep proper records of their radars, and the government actively misled investigators and the public at the time.

It's now widely accepted that the Itavia 870 was downed by a NATO plane, likely French, likely engaged in some sort of anti-Lybic operation.

Yes, but I meant, with all the details, and with all the nations involved taking their own responsibilities. Who knows, maybe in 50 years they will unveil the state secrecy and we'll know it for sure..

Yes: http://en.wikipedia.org/wiki/Iran_Air_Flight_655

Iran Air Flight 655, Siberia Airlines Flight 1812, and of course Korean Air Lines Flight 007, but it was shot down by air-to-air missile.

It wasn't so long ago that Ukraine shot a Russian airliner down (perhaps accidentally, perhaps not):

http://www.nytimes.com/2001/10/14/world/after-9-days-ukraine...

So, the blame is on Russia. https://www.facebook.com/butusov.yuriy/posts/802946763078955

Yuriy Butusov is a Ukrainian chairborne commandо. His opinion on all things Russia is known in advance and so is irrelevant.