Kyiv, Ukraine - Ukrainian President Volodymyr Zelensky said Wednesday that Russia was "playing with the lives of Ukrainian prisoners" after Moscow accused Kyiv of downing a military plane carrying dozens of its own captured soldiers.

Ukrainian President Volodymyr Zelensky

Moscow said 74 people died -- 65 of them Ukrainian prisoners of war being flown to a scheduled exchange -- when a military transport plane was shot down in the western Belgorod region near the border with Ukraine earlier on Wednesday.

"It is obvious that the Russians are playing with the lives of Ukrainian prisoners, with the feelings of their relatives and with the emotions of our society," Zelensky said in an evening address on the incident.

He did not confirm or deny Russia's claims, but said it had been a "very difficult day."

"We need to establish all the clear facts. As much as possible, given that the downing of the plane occurred on Russian territory, which is beyond our control," he said in a video published on social media.

He also called for an international investigation into what brought down the plane.

Russia immediately blamed Ukraine for the incident, calling it a "terrorist act."

In a series of carefully-worded statements, various military agencies in Kyiv confirmed a prisoner exchange had been scheduled to take place and said Russia was responsible for protecting Ukrainian POWs in its custody, while vowing to continue targeting Russian military facilities and planes in the Belgorod region.

But Kyiv is yet to say whether Ukrainian POWs were killed in the crash or if the plane was downed by Ukrainian weapons.

Zelensky said he had instructed various state agencies to investigate the crash.