The AP is reporting that Ukraine's security forces have produced a pair of intercepted phone calls that they say provide evidence that pro-Russian rebels are responsible for the attack. At this time, the recordings are unverified.
Here's the audio, reportedly between a Ukrainian rebel commander and a Russian military intelligence officer:
Here's a translated transcript, featuring the rebel commander (Igor Bezler) and the security officer (Vasili Geranin):
Igor Bezler: We have just shot down a plane. Group Minera. It fell down beyond Yenakievo.
Vasili Geranin: Pilots. Where are the pilots?
IB: Gone to search for and photograph the plane. It's smoking.
VG: How many minutes ago?
IB: About 30 minutes ago.
A second call, reportedly between two unnamed rebel fighters, indicates that the attack was carried out by insurgents approximately 15 miles north of the site of the crash.