Two Ukrainian military jets were shot down in rebel-held eastern regions.
The two Sukhoi fighter jets were shot down near Savur Mogila in eastern Ukraine, said a spokesman of the Ukrainian military establishment.
Xinhua reports that he did not provide any details about the fate of the pilots.
Meanwhile, the first planes carrying bodies from flight MH17 have left Ukraine for The Netherlands, which is holding a day of mourning for the 298 victims.
Experts there will begin to identify the dead, most of whom were Dutch.
Pro-Russian rebels have been widely accused of shooting down the Malaysia Airlines plane on July 17.
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Although 200 bodies have so far been accounted for, experts believe there could be more left at the crash site.
On Wednesday morning, 40 coffins were slowly loaded on to two military planes at Kharkiv Airport.
In a separate process, according to the BBC, the "black box" flight-data recorders from MH17 have arrived in the UK, where they will be examined at the headquarters of the Air Accidents Investigation Branch in Farnborough.
Earlier in Washington, officials from the Office of the Director of National Intelligence presented evidence they had gathered on the involvement of the rebels.
"It's a solid case that it's an SA-11 [missile] that was fired from eastern Ukraine under conditions the Russians helped create," said the officials, who requested that their names not be reported.