Russian President Vladimir Putin apologized to the President of Azerbaijan for the crash of the civilian airliner that killed 38 people, the Kremlin said Saturday.

“Vladimir Putin apologized for the fact that the tragic incident occurred in Russian airspace,” the Kremlin said.

The airliner had “repeatedly attempted to land” at the Grozny airport, Putin told Ilham Aliyev, which at the time was being “attacked by Ukrainian combat drones.”

Russian air defense systems “repelled these attacks,” Putin said.

He did not say if the plane was hit by Russian air defenses but Kremlin said that an investigation was underway and civilian and military specialists were being interrogated.

Two U.S. military officials told NBC News on Friday that the plane may have been hit by Russian missiles, saying they had intelligence indicating that Russians may have misidentified the plane and shot it down.

The intelligence suggested that Russians believed the airliner was a drone, partly because of irregular flight pattern, the officials said.

The Azerbaijan Airlines plane crash landed near the city of Aktau in Kazakhstan on Christmas day, killing 38 of the 67 on board.

The Embraer 190 experienced “physical and technical external interference,” the carrier said Friday, while the plane was en route from the Azerbaijan capital Baku, to Grozny, the capital of Chechnya, Russia.