Russia's President Vladimir Putin has apologised to the president of neighbouring Azerbaijan for the downing of a commercial airliner in Russian airspace, in which 38 people were killed - but stopped short of saying Russia was responsible.

In his first comments on the Christmas Day crash, Putin said the "tragic incident" had occurred when Russian air defence systems were actively repelling Ukrainian drones.

It had been reported the plane came under fire from Russian air defence systems as it tried to land in Chechnya - forcing it to divert across the Caspian Sea.

It crash-landed in Kazakhstan, killing 38 of the 67 on board.

The Kremlin released a statement on Saturday noting Putin had spoken to Azerbaijan's president Ilham Aliyev by phone.

"(President) Vladimir Putin apologised for the tragic incident that occurred in Russian airspace and once again expressed his deep and sincere condolences to the families of the victims and wished a speedy recovery to the injured," the statement said.

Prior to Saturday, the Kremlin had not yet commented on the crash. But Russian aviation authorities had said the situation in the region was "very complicated" due to Ukrainian drone strikes on Chechnya.

Aviation experts and others in Azerbaijan believe the plane's GPS systems were affected by electronic jamming and it was then damaged by shrapnel from Russian air defence missile blasts.

Survivors had previously reported hearing loud bangs before the plane crashed, suggesting it had been targeted.

Azerbaijan had not officially accused Russia this week, but the country's transport minister said the plane was subject to "external interference" and damaged inside and out as it tried to land.

US defence officials on Friday had also said they believed Russia was responsible for the downing.

In Saturday's phone call, Putin acknowledged that the Azerbaijan Airlines plane had repeatedly tried to land at Grozny airport in Chechnya on 25 December.

At the time, Grozny, Mozdok and Vladikavkaz were being attacked by Ukrainian drones and Russian air defense systems had repelled those attacks, Putin said according to the Kremlin's statement.

Moscow noted that Russian investigators had launched a criminal investigation. Azerbaijan had already announced it would launch an investigation.