there is video of the moment the 'object' hit the il-76. it appears to carry on in a straight tajectory after impact. this seems odd for a manpad. lucky unguided rocket? some reports say it was gunfire, so all bases covered so far.
Edit: latest sources saying two empty Igla launchers found. that may explain one hitting, one missing - the latter being the bright object that carried straight on.
BBC News - Ukraine footage 'shows burning plane wreckage'
not a good escalation however it was brought down.