The tail of the Il-76 emergencies ministry plane was found north of Irkutsk, in the region straddling Russia's Lake Baikal, where catastrophic fires have been raging for weeks.
Rescuers found six bodies and both the data and voice flight recorders at the scene, ministry spokesman Alexei Vagutovich told Interfax news agency.
Investigators were also at the site following Saturday's launch of a criminal probe into the crash.
Earlier, the ministry said ten people were on board the plane, which stopped making contact early on Friday.
Footage from the crash site showed the tail of the transport plane lying on charred ground with the rest of the fuselage apparently completely burned.
A Russian aviation agencies source told TASS news agency that the plane most likely lost control because of interference from hot air from the wildfire that it was trying to douse with water.
"It's possible that hot air from the wildfires got into the engines, the plane lost propulsion and could not gain altitude, hit the top of the trees and fell," the source was quoted as saying.
The plane's tail was discovered by another firefighter on Sunday morning, said the Russian forestry agency's aviation unit.
Last week another firefighter died on duty in Russia's far-eastern Kamchatka region, the regional government revealed.
The forestry agency's aviation unit said today that over 43 thousand hectares of forest land is burning in Russia, mostly in Siberia.
But Russia's Greenpeace which monitors wildfires via satellite data said government figures are vastly underestimated, with 415 thousand hectares burning in Irkutsk region alone.
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