Azerbaijan Airlines officials say they are grounding all flights to Russia after the Christmas Day plane crash that left 38 passengers dead.

In a statement released on Friday, the airline said it would be suspending flights to seven cities in Russia, according to Agence France Presse. Officials for the company said that the decision to halt service was made after “taking into account the initial results of the investigation into the crash… and taking into account flight safety risks.”

Azerbaijan Airlines also cited preliminary results of an investigation found that the cause of the crash was a result of the aircraft experiencing “physical and technical external interference,” according to a report from CNN.

According to a report published Thursday by 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.

The pilots requested an emergency landing but could not 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.

On Friday, Russian officials said the passenger plane was diverted from its destination at the city of Grozny due to Ukrainian drones in the area and fog conditions, according to CNN.

“Ukrainian combat drones were carrying out terrorist attacks on civilian infrastructure in the cities of Grozny and Vladikavkaz,” the head of Russia’s Federal Air Transport Agency, Dmitry Yadrov, said.

He also claimed that the pilots had attempted to land at Grozny twice before they decided to fly across the Caspian Sea in Kazakhstan.

The Ukrainian foreign minister, Andrii Sybiha, said in a statement on Friday that the Russian press has not been truthful about the cause of the crash.

“[Moscow] forced the damaged jet to cross the sea, most likely in an attempt to conceal evidence of their crime,” he said, also calling for an impartial investigation.

“Photos and videos from the cabin and after the crash are a smoking gun.”