Russia has accused Ukraine of deliberately shooting down a Russian military transport plane carrying 65 captured Ukrainian soldiers to a prisoner exchange in what it called a barbaric act of terrorism that had killed 74 people.
Ukraine called for full clarification of the circumstances of the incident and did not directly confirm it had shot down the plane.
Ukrainian President Volodymyr Zelenskiy, in his evening address said: "It is clear that the Russians are playing with the lives of Ukrainian prisoners, the feelings of their loved ones and the emotions of our society."
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 Russian city of Belgorod near the Ukrainian border.
After a long pause, the Ukrainian military said it would continue to destroy Russian military transport aircraft it believed were carrying missiles with which to strike Ukraine.
It said it had noticed more Russian military transport aircraft landing in Belgorod, something it linked to Russian missile strikes on Kharkiv and other Ukrainian cities.
Air Force Commander Mykola Oleshchuk accused Russia of trying to undermine international support for Ukraine.
"Ukraine has the right to defend itself and destroy the means of the aggressors' aerial attack," he said.
The Russian defence ministry said the exchange was to have taken place on Wednesday afternoon at the Kolotilovka border checkpoint and Ukraine knew a transport plane carrying captured Ukrainian soldiers was expected at the Belgorod airfield.
"By committing this terrorist act, the Ukrainian leadership has showed its true face. It disregarded the lives of its own citizens," the ministry said in a statement.
The UN Security Council will gather at Russia's request on Thursday to discuss the incident.
Ukraine's GUR military intelligence agency said Ukraine had not been asked to ensure airspace security around Belgorod unlike previous swaps and had not been told what transport and which routes would be used.
"We may be talking about planned and deliberate actions by Russia to destabilise the situation in Ukraine and weaken international support for our state," GUR said on Telegram.
Russia's defence ministry said radar operators had detected the launch of two Ukrainian missiles at the time of the crash.
If the details are confirmed, it would be the deadliest incident of its kind inside Russia's internationally recognised borders since it launched its "special military operation" against Ukraine in February 2022.
Ukraine's intelligence agency confirmed a prisoner swap had been planned for Wednesday and said the captured Russian servicemen had been delivered to the agreed exchange point on time and were safe.
"Landing a transport plane in a 30km combat zone cannot be safe and in any case must be discussed by both sides because otherwise it jeopardises the entire exchange process," it said.
Video posted on Telegram by Baza, a channel linked to Russian security services, and verified by Reuters, showed a large aircraft falling to the ground near the village of Yablonovo in Belgorod region and exploding in a fireball.
Andrei Kartapolov, a member of Russia's parliament and a retired general, told the SHOT news outlet it was impossible for operators of Ukrainian surface-to-air missile systems to mistake transport planes for military planes or helicopters as targets.
"It was done deliberately to sabotage the prisoner exchange," said Kartapolov, saying a second Russian Il-76 transport plane carrying about 80 Ukrainian soldiers to the exchange had managed to turn around.
The Belgorod region, which borders Ukraine, has come under frequent attack from Ukraine in recent months, including a December missile strike that killed 25 people.
