As huge plumes of black smoke rose up near a village in eastern Ukraine, the fate of the passengers aboard the plane wasn't immediately known.
Anton Gerashenko, an adviser to Ukraine's interior minister, said on his Facebook page the plane was flying at an altitude of 10,000 meters (33,000 feet). He also said it was hit by a missile fired from a Buk launcher, which can fire missiles up to an altitude of 22,000 meters (72,000 feet).
The Donetsk region government said a plane crashed Thursday near a village called Grabovo, which it said is currently under the control of armed pro-Russian separatists. The region where the flight was lost has seen severe fighting between Ukrainian forces and pro-Russia separatist rebels in recent days.
Both the president of Ukraine and a separatist leader denied shooting anything down Thursday.
Separatist leader Andrei Purgin told The Associated Press that he was certain that Ukrainian troops had shot it down but gave no explanation for that statement.
Purgin said he was not aware of whether rebel forces owned Buk missile launchers, but even if they did, there had no fighters capable of operating it.
AP Airlines Writer Scott Mayerowitz in New York contributed to this report.
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