Speculation swirls over deadly crash of Azerbaijan Airlines plane. Here’s what we know.

(CNN) — Azerbaijan held a day of mourning on Thursday for the dozens of victims of an airliner crash in Kazakhstan, as questions were being asked over the cause of the disaster.

The reasons that Azerbaijan Airlines flight J2-8243 came down are still unknown. Reuters reported Thursday that the plane was downed by a Russian air defense system, citing multiple unnamed sources in Azerbaijan with knowledge of the investigation.

Officials from Azerbaijan, Kazakhstan and Russia, three countries linked to the disaster, urged people not to speculate about the crash until investigations have concluded.

Here’s what we know about the crash so far.

What was the route of the plane?

The Azerbaijan Airlines flight was traveling from the Azerbaijani capital Baku to Grozny, the capital city of the southern Russian republic Chechnya before it made an emergency landing approximately 3 kilometers (1.8 miles) from Aktau, Kazakhstan, the carrier said on Wednesday.

Russian state media reported that the plane was rerouted due to heavy fog in Grozny.

Officials did not immediately explain why the plane had crossed the Caspian Sea, when Baku and Grozny are to its west and Aktau is to its east.

Flight-tracking website Flightradar24 said in a social media post that the aircraft was “exposed to GPS jamming and spoofing near Grozny.” GPS jamming can significantly hinder a plane’s ability to navigate and communicate, Flightradar24 said, creating potential safety risks.

Data and video of the crash also “indicate possible control issues with the aircraft,” Flightradar24 said.

How many survived the crash?

At least 38 of the 67 people on board the plane were killed in the crash, Kazakh authorities confirmed, including two pilots and a flight attendant.

Some 29 survivors, two of whom are children, were pulled from the wreckage, Kazakhstan’s Deputy Prime Minister Kanat Bozumbayev said.

Of those flying on the plane, 37 of the passengers were Azerbaijan citizens and 16 were from Russia, along with six from Kazakhstan and three from Kyrgyzstan, according to preliminary data from Kazakhstan’s transport ministry. None of those who survived were Kazakh nationals, Bozumbayev said.

Azerbaijani state news agency AZERTAC reported that 12 survivors will be transported back to Azerbaijan on Thursday, five of whom are in a “serious but stable condition.” These five people will be flown back by a special aircraft from the country’s Ministry of Emergency Situations, AZERTAC said.

NATO’s spokesperson Farah Dakhlallah said in a social media post that the alliance’s “thoughts and prayers are with the families and victims” of the disaster. “We wish those injured in the crash a speedy recovery and call for a full investigation,” she wrote.

What was the cause of the crash?

Video and images of the plane after it crashed show perforations in its body that look similar to damage from shrapnel or debris. The cause of these holes has not been confirmed.

Azerbaijan Airlines initially told AZERTAC that the incident was caused by the aircraft colliding with a flock of birds, the outlet reported. Russia’s Federal Air Transport Agency Rosaviatsia also said the plane crashed after colliding with birds.

However, Andriy Kovalenko, the head of Ukraine’s Center for Countering Disinformation, part of the National Security and Defense Council of Ukraine, disputed this, claiming on social media that the plane was “shot down by a Russian air defense system.”

The crash came shortly after Ukrainian drone strikes hit southern Russia. Drone activity has shut airports in the area in the past and the nearest Russian airport on the plane’s flight path was closed on Wednesday morning.

“Russia should have closed the airspace over Grozny but failed to do so,” Kovalenko said, speculating that authorities will try to cover up the real reason behind the crash, including the holes in the plane, as it would be “inconvenient” to blame Russia.

Justin Crump, an intelligence, security and defense expert and the CEO of risk advisory company Sibylline, told BBC Radio 4 on Thursday that the plane being fired at by Russia is “the best theory that fits all the available facts that we know of.” Crump added that Russian air defenses were active in Grozny around the time that the plane was damaged.

“I don’t think this is deliberate at all,” he noted, pointing out that Russia is “very worried” about longer-range active Ukrainian drones that are “very often not getting shot down.”

Osprey Flight Solutions, a UK-based company that analyzes security risks in the aviation sector, also said in an alert to airlines that the flight “was likely shot down by a Russian military air-defense system,” according to the Wall Street Journal.

What are authorities saying?

Kremlin spokesman Dmitry Peskov said on Thursday that it would be wrong to speculate about the cause of the plane crash before an investigation had been carried out, according to Russian state media RIA Novosti.

Maulen Ashimbayev, chairman of Kazakhstan’s senate, said Thursday that “the nature of these damages and the causes of the disaster are currently unknown.”

A commission has been set up to investigate the crash, involving representatives from Kazakhstan, Azerbaijan and Russia, Ashimbayev said.

Kanat Bozumbayev, Kazakhstan’s deputy prime minister, said that “even the preliminary cause cannot be determined yet, as specialists are needed for that.”

“They will conduct the work, and then it will be clear,” Bozumbayev said Thursday.