Russia on Wednesday accused Ukraine of shooting down a military transport plane carrying dozens of Ukrainian detainees headed for a prisoner exchange, killing everyone on board.
Kyiv confirmed a prisoner swap was due to occur Wednesday, but several hours after the crash said it still had no reliable information on the passengers, as President Volodymyr Zelensky called for an international investigation.
Videos on social media showed a large plane in Russia's western Belgorod region falling from the sky on its side before crashing in a fireball.
Russia's defence ministry said the IL-76 plane was carrying 65 Ukrainian soldiers captured in Russia's offensive, as well as six crew and three escorts.
It claimed Ukrainian forces stationed in the Kharkiv border region had fired two missiles at the transport aircraft and described the incident as a "terrorist act".
"We currently do not have reliable or comprehensive information on who was on board the plane or in what number," Ukraine's main intelligence agency said in a statement.
Zelensky, in an evening address, did not confirm or deny Moscow's accusations, but stressed that Russia was "playing with the lives of Ukrainian prisoners, with the feelings of their relatives and with the emotions of our society."
"We need to establish all clear facts, as much as possible given that the plane crash occurred on Russian territory -- beyond our control," he said.
- UN Security Council meeting -
Around the time Zelensky called for an international investigation, the UN Security Council agreed to meet Thursday at 5:00 pm (2200 GMT) to discuss Moscow's accusations regarding the plane.
AFP could not independently verify the Russian claims but the incident would represent one of the single most deadly episodes of the full-scale conflict in weeks.
Russia's defence ministry said the crash had come hours ahead of the planned prisoner exchange at a border crossing in Belgorod.
"The Ukrainian leadership was well aware that, in accordance with established practice, the Ukrainian servicemen to be exchanged would be transported by military transport aircraft to the Belgorod aerodrome today," it said.
Ukraine's intelligence agency denied this and accused Russia of "endangering the lives and safety of prisoners".
- Muted reaction in Kyiv -
Ukrainian media initially cited defence sources saying Ukraine's army had downed the plane, and that it was carrying missiles. The claim was later retracted.
In a carefully worded statement published after the crash, the Ukrainian army said it would continue to target Russian aircraft in Belgorod region.
It said a number of shelling attacks on Ukrainian territory were "directly related" to Russian military transport aircraft flying to Belgorod airfield.
The crash occurred in Korochansky district, northeast of the Belgorod region's capital at around 0800 GMT, governor Vyacheslav Gladkov said.
He added that the aircraft was downed in a field and the area had been closed off while investigators and emergency services worked at the scene.
"The plane crashed far away from the village. It was very loud and very scary," said Maria Mexentseva, a resident of nearby Yablonovo.
"We just heard a loud rumble," she told the RIA-Novosti news agency. "There was already smoke, fire and rumbling."
Kremlin spokesman Dmitry Peskov declined to comment on the crash, saying news was still emerging and that authorities would "look into" the incident.
The head of Russian-state broadcaster RT published a list of captured Ukrainian servicemen allegedly on board.
Ukrainian civilian casualties of the war ticked up on Wednesday, with two people, including a 16-year-old, killed and nine wounded when a Russian rocket hit Girnyk village in the eastern Donetsk region, Donetsk regional head Vadim Filachkine said, accusing Moscow of targeting civilians.
A strike in the southern city of Kherson wounded six people, local officials said.
- POWs sensitive issue -
The issue of prisoners of war is sensitive in both countries.
Despite full-scale hostilities, the two sides have carried out 49 prisoner exchanges since the conflict began almost two years ago.
Kyiv says more than 8,000 Ukrainians remain in Russian captivity, including civilians.
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 Ukraine's Donetsk region.
Since Moscow launched large-scale hostilities in Ukraine in February 2022, several Russian military aircraft have crashed, and Ukraine has also claimed to have shot down Russian war planes.
In Russia, the plane carrying Wagner mercenary group leader Yevgeny Prigozhin crashed last August on a flight from Moscow to St Petersburg.
Moscow denied involvement, claiming instead that the plane crashed because its passengers detonated a grenade on board.