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.
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 told Russian news agencies.
"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.
Vyacheslav Volodin, the top lawmaker in Russia's lower house of parliament, said the plane had been "shot down" by Kyiv and blamed Western missiles.
"They shot their own soldiers in the air. Their own," Volodin told lawmakers in a plenary session. "Our pilots, who were carrying out a humanitarian mission, were shot down."
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.
Gladkov had earlier announced a missile alert over the region, but it was not clear if the two events were connected.
In Kyiv, local media initially cited sources in the Ukrainian military as saying that its army downed the plane, and that it was transporting missiles.
But that claim was later retracted.
The issue of prisoners of war is sensitive in both countries.
In 2022, Russia and Ukraine accused each other of carrying out deadly bombardments on a jail holding dozens of captured Ukrainian servicemen in Kremlin-controlled Olenivka, in eastern Ukraine's Donetsk region.
Both Moscow and Kyiv blamed each other for the incident, which President Volodymyr Zelensky called a "Russian war crime".
- Strikes on Ukraine -
Moscow and Kyiv have also recently accused each other of a sharp escalation in attacks on civilian areas over the past two months.
Russian strikes wounded nine people in the eastern Ukrainian region of Kharkiv, the region's governor said Wednesday.
Regional governor Oleg Sinegubov said Moscow's forces had fired S-300 surface-to-air missiles at the city, which lies next to Ukraine's border with Russia.
Russian forces had aimed to wrest control of Kharkiv, Ukraine's second-largest city, early in their invasion, launched in February 2022.
But Ukrainian forces pushed back Moscow's army, which has been routinely shelling the city since.
Separately, the governor of the southern Kherson region said Russian forces had killed a total of five residents of his region over the course of the day before.
Six more people were wounded across the region, which the Kremlin claims is part of Russia, the governor, Oleksandr Prokudin, said on social media.
Both Russian and Ukraine have stepped up strikes on each others' cities and critical infrastructure.
Kyiv has urged its allies to help bolster its air defence systems to ward off Russian attacks.