From USAToday:
the plane was flying at an altitude of 33,000 feet when it was hit Thursday by a missile fired from a Buk launcher, the Associated Press reports.
BUK, also known as SA-17 GRIZZLY, is a mobile anti-aircraft system mounted usually on a tracked vehicle or truck that can simultaneously track and strike six targets flying from different directions and at different altitudes, according to military thinktank Globalsecurity.org.
A similar launcher was seen by AP journalists near the eastern Ukrainian town of Snizhne earlier Thursday.