Russia alleged that Kyiv shot down the plane with two missiles and said the prisoners of war were headed for an exchange. Kremlin spokesman Dmitry Peskov described it as “a totally monstrous act.”

Ukraine responded by accusing Russia of spewing propaganda, cast doubt on the fact that POWs were aboard — and put forward their own theories, including implying that the plane may have posed a threat.

Mykola Oleshchuk, Ukraine’s Air Force Commander, alleged that “rampant Russian propaganda is directing a fake stream of information to the international audience, attempting to discredit Ukraine in the eyes of the global community.”

Ukrainian officials didn’t dispute that the plane went down and they confirmed a prisoner exchange was due to happen Wednesday — but said it was called off. President Volodymyr Zelenskyy said Ukraine would push for an international investigation.

As the conflict approaches the two-year mark, the 1,500-kilometer (930-mile) front line has been largely static amid a second winter of fighting. With both sides seeking to replenish their weapons stockpiles, the war recently has focused on long-range strikes.

Earlier this month, in a significant blow to the Kremlin’s forces, the Ukrainian air force claimed to have shot down a Russian early warning and control plane that can spot targets up to 650 kilometers (400 miles) away and a key command center aircraft that relays information to troops on the ground.

The discovery of the transport plane’s flight recorders was reported Thursday by the state-owned RIA Novosti news agency, citing emergency services.

Ukrainian officials have noted that Moscow didn’t ask for any specific airspace to be kept safe for a certain length of time, as it has in past prisoner exchanges.

Without mentioning the crash, the General Staff of the Armed Forces of Ukraine said that the country would target any Russian military transport plane believed to be delivering missiles, especially near the border.

Russian Foreign Minister Sergey Lavrov called for an emergency meeting of the U.N. Security Council, which was expected to take place on Thursday afternoon in New York.

Andrei Kartapolov, head of the defense affairs committee in the lower house of the Russian parliament, said Russia would continue exchanging prisoners despite the crash.

“We can’t abandon our boys and so we will speak to the devil himself to get them out,” he told reporters.

Meanwhile, Ukraine’s largest oil and gas company, Naftogaz, said Thursday that one of its data centers had come under a large-scale cyberattack that shut down the company’s web sites and call centers.