Russian President Vladimir Putin has said: "Undoubtedly, the government in whose air space this happened bears responsibility for this terrible tragedy," according to a Kremlin statement (Russian).
He also said "this tragedy would not have happened if there were peace in this land, or in any case, if [Kiev] had not renewed hostilities in south-eastern Ukraine."
He said that he has given "instructions to the military so that they have all the necessary help in the investigation of this crime", and that he's requested the government's civilian agencies to assist as best in can in the investigation. He added that "no one has the right" to make conclusions without comprehensive, "objective information about the incident".
Putin also reiterated his condolences for victims' families, and observed a moment of silence.