Russia has accused Ukraine of shooting down a military transport plane carrying dozens of Ukrainian prisoners headed for a prisoner exchange, killing everyone on board.
Kyiv confirmed that a prisoner exchange was due to take place today, but said it had no reliable information on the passengers of the downed plane.
Moscow said 65 captured Ukrainian soldiers were killed when an Ilyushin-76 plane was shot down in its western Belgorod region, close to the border with Ukraine, ahead of a planned prisoner exchange between the two sides.
"We currently do not have reliable or comprehensive information on who was on board the plane or in what number," Ukraine's main intelligence directorate said in a statement.
Without commenting on whether Ukrainian prisoners of war were on board, the intelligence agency accused Moscow of endangering the lives of its captured soldiers.
"Ukraine was not informed about the number of vehicles, routes and forms of delivery of prisoners," it said.
"It is known that prisoners are delivered by air, rail and road. This may indicate deliberate actions by Russia aimed at endangering the lives and safety of prisoners."
Ukrainian government agencies have issued a number of carefully-worded statements regarding the incident in the hours since the plane crashed this morning.
Kyiv also said Russia was responsible for ensuring the security of Ukrainian prisoners and that Moscow did not inform it about plans to transport any captured soldiers in the Belgorod region where the plane was shot down.
"The Ukrainian side was not informed about the need to ensure the security of the airspace in the area around the city of Belgorod at a set time, as has been done many times in the past," the intelligence directorate said.
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.
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 11am Moscow time (8am Irish time), 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.
"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.
"By committing this terrorist act, the Ukrainian leadership has showed its true face. It disregarded the lives of its own citizens," it added.
None of the details in relation to those whom Russian officials say were on board have been verified.
Ukraine said it would continue to target Russia's military in the Belgorod region, hours after Moscow accused it of shooting down the plane.
In a statement that did not mention the crash, the Ukrainian army said it would "continue to take measures to destroy delivery vehicles and control airspace to eliminate the terrorist threat, including in the Belgorod-Kharkiv direction".
Vyacheslav Volodin, the leading MP 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," Mr Volodin told MPs 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," Mr Gladkov said.
Mr 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.
Russia today called for an emergency UN Security Council session following the crash.
Russian Foreign Minister Sergei Lavrov told a press conference at the United Nations that Russia had called for the meeting to be held at 3pm. Eastern time (8pm Irish time).
Andrei Kartapolov, a politician in Russia's parliament and a retired general, said in a TV interview with the SHOT outlet that it was impossible for the 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 Mr Kartapolov, saying a second Russian Il-76transport plane carrying around 80 Ukrainian soldiers to the exchange had managed to turn around.
The Russian defence ministry said its radar operators had detected the launch of two Ukrainian missiles at the time the plane was downed.
Mr Kartapolov, who has close links to the Russian defence ministry, said the plane had been downed by three missiles of either US or German manufacture.
He said it had not been escorted by Russian fighter planes because the flight had been agreed with the Ukrainians.
If the details are confirmed, it would be the deadliest incident of its kind inside Russia's internationally recognised borders during the almost two-year-old war.
Reuters could not immediately verify details of who was on board the downed plane, but Moscow and Kyiv have regularly swapped prisoners since Russia began what it calls its "special military operation" in Ukraine in February 2022.
Russian state media published a list of names of the 65 captured Ukrainian soldiers it said were on board along with their dates of birth.
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".
It comes as Ukrainian officials said Russian strikes wounded nine in Kharkiv in eastern Ukraine, just after a Russian missile barrage across the country that claimed more than a dozen lives.
The new Russian bombardments struck Kharkiv yesterday, hours after Moscow's missile attack killed at least 18 and wounded around 130 people.
The regional governor Oleg Sinegubov said Russian forces had fired S-300 surface-to-air missiles at the city, which lies next to Ukraine's border with Russia.
"As a result of the impact, nine people were injured, including one child, a four-year-old girl, who was given help at the scene," he said.
"Four people were hospitalised - two men and two women," he added, noting that residential buildings, municipal offices and an educational facility were damaged.
Russian forces had aimed to wrest control of Kharkiv, Ukraine's second-largest city, early in their invasion, launched in February 2022.
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.
