Government insiders from Azerbaijan have placed blame directly on Russia for the fatal crash of a commercial airliner over Kazakhstan on Christmas Day, claiming a surface-to-air missile struck the plane.

According to a report from Euro News, sources from within the Azerbaijani government said that Azerbaijan Airlines Flight 8432 was flying through drone activity over the city of Grozny in Chechnya when the plane was struck by the missile which was fired from a Pantsir-S air defense system. The aircraft was severely damaged as a result, with passengers injured from shrapnel.

CNN also reported later Thursday that a U.S. official told the news outlet that early indications suggest a Russian anti-aircraft system may have downed the plane. The official said it is possible that poorly trained Russian units may have fired negligently on Ukrainian drones.

Russian sources tell Euro News that as Flight 8432 was passing over the region, their air defense forces were actively making attempts to shoot down Ukrainian drones. The attack was confirmed to have taken place over Grozny by the head of the Security Council of the Chechen Republic, Khamzat Kadyrov.

The pilots requested an emergency landing but were not allowed to touch down at any Russian airports. According to Azerbaijani sources, they were ordered to fly across the Caspian Sea to make their landing toward Kazakhstan. Thirty-eight passengers were killed after the plane crashed near the city of Aktau. Only 29 survived the fiery crash.

A national day of mourning was held on Thursday across Azerbaijan for those who perished.

“This is a great tragedy that has become a tremendous sorrow for the Azerbaijani people,” President Ilham Aliyev said on Thursday. He has also said he has formed a commission that will launch a criminal investigation into the cause of the crash.

Russian officials cautioned against giving any credence to “hypotheses” about the cause of the crash. 

“It would be wrong to put forward any hypotheses before the investigation’s conclusions,” Kremlin spokesman Dmitry Peskov said, according to the BBC. “We, of course, will not do this, and no one should do this. We need to wait until the investigation is completed.” 

Shortly after the incident, state-controlled TV in Russia offered a hypothesis of its own and said a strike from a flock of birds likely caused the crash.

Kazakh authorities have recovered the flight data recorder and begun investigating the crash.

Aviation experts told the BBC that the damage pattern is consistent with air defense strikes.

“It looks very much like the detonation of an air defense missile to the rear and to the left of the aircraft if you look at the pattern of shrapnel that we see,” Justin Crump of Sibylline, a risk advisory company, said during an interview with BBC Radio 4.

If the claims by the Azerbaijani Government are confirmed, it would mark the second time in a decade that a commercial airliner was destroyed by Russian military forces after Malaysia Airlines Flight MH17 was downed over Ukraine in 2014.