The British Guardian newspaper has 'chapter & verse' on the rebel website which, according to that newspaper, initially claimed responsibility for shooting down an aeroplane violating its airspace. Apparently that site has since been taken down, but not before it was copied by the Western media. If correctly copied and translated, the rebels thought they were shooting down a Ukrainian transport plane, and that Ukraine had been warned not to invade the rebels' airspace.
Malaysia Airlines plane MH17 crashes in Ukraine - live updates | World news | theguardian.com