A Russian military transport plane has crashed near the southern city of Belgorod, close to the border with Ukraine, Russian authorities said Wednesday.

The plane was carrying 65 Ukrainian prisoners of war, according to the Russian ministry of defense. NBC News could not independently verify who was on board the flight and has approached Ukraine’s armed forces for comment.

It was not immediately clear what caused the crash or whether anyone survived.

The Ilyushin Il-76 was “performing a scheduled flight” when it came down in the region adjacent to Ukraine’s northeastern border, the defense ministry said in a statement published by the state-run Tass news agency.

“On board were 65 captured military personnel of the Ukrainian Armed Forces transported to the Belgorod region for exchange, as well as six crew members and three accompanying persons,” the statement said.

A team has been sent to the crash site to investigate the cause of the incident, it added.

The Kremlin was looking into the situation, its spokesperson Dmitry Peskov told reporters.

The chair of the Russian parliament’s defense committee, Andrey Kartapolov, said that the plane was was shot down by three air defense missiles of a type supplied to Ukraine by its Western allies.

“The Ukrainian leadership was well aware of the impending exchange and was informed of how the prisoners would be delivered,” he said during a speech in parliament. He did not elaborate on the source of his information.

The two countries regularly carry out exchanges of prisoners, even as they continue to fight along the war’s front lines in Ukraine’s east and south.

Regions across western Russia, including Belgorod, have come under regular attack in recent weeks.

Russian officials have accused Kyiv of carrying out the strikes. Ukrainian officials rarely take public responsibility for attacks on Russian territory or the occupied Crimean Peninsula. However, larger aerial strikes against Russia have previously followed heavy assaults on Ukrainian cities.

Belgorod, the largest Russian city near the border, has a population of about 340,000 people. It is about 60 miles north of Kharkiv, Ukraine’s second-largest city.

This is a breaking news story. Please check back for updates.