Russia has accused Ukraine of deliberately shooting down a Russian military transport plane carrying 65 captured Ukrainian soldiers to a prisoner exchange.
Moscow called it a barbaric act of terrorism that had killed a total of 74 people.
The Russian defence ministry said six Russian crew members and three Russian soldiers had been on the Ilyushin Il-76 military transport plane shot down near the city of Belgorod near the Ukrainian border.
"The Ukrainian leadership was well aware that, in accordance with established practice, Ukrainian servicemen would be transported by military transport aircraft to the Belgorod airfield today to be exchanged," a ministry statement said.
"According to an earlier agreement, this event was to take place in the afternoon at the Kolotilovka checkpoint on the Russian-Ukrainian border," it added.
The Russian defence ministry said its radar operators had detected the launch of two Ukrainian missiles at the time the plane was downed.
Meanwhile, Ukraine's military intelligence said Kyiv was not asked to ensure air space security on Wednesday around the Belgorod area as had been the case during previous prisoner of war swaps with Moscow.
In a post on Telegram, it said Russia's accusations that Kyiv shot down the plane could be "a planned action to destabilise the situation in Ukraine and weaken international support for our state".
The agency also said it had no reliable information on who was onboard the crashed plane.
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