Russia said Wednesday that an IL-76 military transport plane carrying 65 Ukrainian prisoners of war had crashed in the western Belgorod region, bordering Ukraine.
Russian parliament speaker accused Kyiv of shooting down the plane carrying POWs.
Unverified videos on social media showed a large plane, purportedly in the Belgorod region, falling from the sky on its side before crashing in a fireball.
"At around 11 am Moscow time (0800 GMT), an IL-76 aircraft crashed in the Belgorod region during a routine flight," Moscow's defence ministry was quoted as saying by the RIA-Novosti news agency.
"On board were 65 captured Ukrainian army servicemen being transported to the Belgorod region for exchange, six crew members and three escorts," it said.
AFP was not able to immediately verify Russia's claim, and the fate of the passengers was not immediately clear.
The crash occurred in the Korochansky district, northeast of the region's capital, regional governor Vyacheslav Gladkov said on Telegram.
"Now an investigation team and emergency services are working on the site. I have changed my working schedule and travelled to the district," Gladkov said.
There was no immediate official reaction in Kyiv, but local media cited sources in Ukraine's defence forces as saying that its armed forces downed the plane, and that it was transporting missiles.