The Russian government has cautioned against promoting "hypotheses" about the cause of the crash of a Russia-bound passenger plane that killed 38 people in Kazakhstan on Wednesday.

Footage of the wrecked fuselage appeared to indicate shrapnel damage and some aviation experts suggested the Azerbaijani Airlines plane may have been been hit by air defence systems over the Russian republic of Chechnya.

Before it went down near the Kazakh city of Aktau, the plane was diverted across the Caspian Sea, from its destination in Chechnya to western Kazakhstan.

Twenty nine of the 67 people on board survived. Azerbaijan held a national day of mourning on Thursday for the victims of the crash.

"This is a great tragedy that has become a tremendous sorrow for the Azerbaijani people," President Ilham Aliyev said on Thursday.

In Moscow, Kremlin spokesman Dmitry Peskov said: "It would be wrong to put forward any hypotheses before the investigation's conclusions. We, of course, will not do this, and no-one should do this. We need to wait until the investigation is completed."

The Embraer 190 aircraft took off from the Azerbaijani capital Baku on Wednesday morning. It was due to fly to Grozny in Chechnya but it was diverted because of fog, the airline said.

A surviving passenger told Russian TV he believed the pilot had tried twice to land in dense fog over Grozny before "the third time, something exploded... some of the aircraft skin had blown out".

The plane was redirected to Aktau airport, some 450km (280 miles) to the east. Footage shows the aircraft heading towards the ground at high speed 3km (1.9 miles) short of the runway, before bursting into flames as it lands.

Kazakh authorities have recovered the flight data recorder and an investigation in under way. Shortly after the crash, reports from Russian state-controlled TV said the most likely cause was a strike from a flock of birds.

But that kind of collision typically results in the plane gliding towards in the nearest airfield, aviation analyst Richard Aboulafia told Reuters news agency. "You can lose control of the plane, but you don't fly wildly off course as a consequence," he said.

Justin Crump of risk advisory company Sibylline said the pattern of damage inside and outside the plane indicated that Russian air defence active in Grozny may have caused the crash.

"It looks very much like the detonation of an air defence missile to the rear and to the left of the aircraft, if you look at the pattern of shrapnel that we see," he told BBC Radio 4.

Authorities in the nearby Russian regions of Ingushetia and North Ossetia reported drone strikes on Wednesday morning.

The head of Kazakhstan's senate, Ashimbayev Maulen, stressed that the cause of the crash was still unknown.

"None of these countries - Azerbaijan, Russia or Kazakhstan - is interested in hiding information. All information will be made available to the public," he said.

Those on board were mostly Azerbaijani nationals, but there were also some passengers from Russia, Kazakhstan, and Kyrgyzstan.

Video footage showed survivors crawling out of the wreckage, some with visible injuries. The injured are being treated in hospital and 11 are in intensive care, AFP news agency reported.

Embraer, a Brazilian manufacturer, is a smaller rival to Boeing and Airbus, and has a strong safety record.