An investigation into the fatal crash of an Azerbaijan Airlines flight in Kazakhstan earlier this week suggests that the crash occurred after “external physical and technical interference” with the passenger plane, the airline said Friday.

The Embraer 190 crashed near the Kazakh city of Aktau on Wednesday, killing 38 of the 67 people on board, while en route from Baku, the capital of Azerbaijan, to Grozny, the capital of Chechnya, Russia.

According to a US official, initial indications indicate that the plane may have been hit by a Russian anti-aircraft system.

Two U.S. military officials told NBC News on Friday that the U.S. has information suggesting the Russians may have misidentified and shot down the Azerbaijani airliner.

The intelligence indicated that the Russians believed it was a drone and attacked its air defenses, in part because of the plane’s erratic flight direction and altitude, the officials said. Both emphasized that the investigation is still ongoing.

On Thursday, Matthew Borie, chief intelligence officer of air security company Osprey Flight Solutions, told NBC News that “the flight was likely shot down by a Russian air defense system.”

At the time of the incident, Russian air defense forces were defending against a military-grade Ukrainian drone attack in which Russia shot down drones, he said.

While Russian officials have warned against speculation about the cause of the plane crash, the country’s aviation authority said Friday the situation around Grozny in Chechnya was “very complicated” as the plane was diverted to Kazakhstan, where it crashed.

Rosaviatsia, the Russian aviation authority, referred to the presence of “Ukrainian combat drones” around Grozny. Chechnya is close to Ukraine and the ongoing war with Russia.

Rosaviatsia also reported that dense fog in the Grozny airport area resulted in no visibility at an altitude of about 1,600 feet. The pilot was offered alternative airports, but decided to continue to the Kazakh city of Aktau after two unsuccessful attempts to land in Grozny, according to a statement from Dmitry Yadrov, head of Rosaviatsia.

On Friday, Azerbaijan Airlines announced that it had also suspended flights from Baku to five other Russian airports. This decision follows the suspension of flights from Baku to Grozny and Makhachkala introduced on Wednesday.

“The suspension will remain in effect pending the completion of the final investigation,” said a statement posted on the airline’s Telegram channel on Friday.