Azerbaijan Airlines says the preliminary results of an investigation into the crash of its plane in Kazakhstan on 25 December have blamed "physical and technical external interference".

Thirty-eight people died when the Embraer jet came down at high speed, bursting into flames 3km (1.9 miles) short of the runway at Aktau airport.

The plane had originally tried to land at Grozny airport in southern Russia, but witnesses have spoken of an explosion before it was diverted across the Caspian Sea to Kazakhstan.

The head of Russia's civil aviation agency said on Friday that the situation in the Chechen capital was "very complicated" and that a closed-skies protocol had been put in place.

"Ukrainian combat drones were launching terrorist attacks on civilian infrastructure in the cities of Grozny and Vladikavkaz," said Dmitry Yadrov, head of Rosaviatsia, in a video statement posted on Russia's Tass news agency.

"Because of this a 'Carpet plan' was introduced in the area of Grozny airport, providing for the immediate departure of all aircraft from the specified area," he said. "In addition, there was dense fog in the area of Grozny airport."

Azerbaijan Airlines did not detail the physical and technical interference, and the government in Baku has avoided directly accusing Russia, possibly to avoid antagonising President Vladimir Putin.

However, aviation experts and pro-government media in Azerbaijan believe the plane was damaged by shrapnel from Russian air-defence missile explosion.

"These are missile fragments that damaged the hydraulic system. The plane's controls operate based on hydraulics," veteran Azerbaijani pilot veteran pilot Tahir Agaguliev told Azerbaijani media.

Flight attendant Zulfuqar Asadov who was among 29 survivors on the crashed plane told local media that the plane was "hit by some kind of external strike".

"The impact of it caused panic inside. We tried to calm them down, to get them seated. At that moment, there was another strike, and my arm was injured."

In a social media post, Azerbaijan Airlines said it was suspending flights to seven Russian cities in response to the crash "for security reasons".

It had already halted flights to Grozny and Makhachkala in neighbouring Dagestan, but has now added the cities of Sochi, Volgograd, Ufa, Samara and Mineralnye Vody.

Israel's flagship airline, El Al, has meanwhile suspended all flights to Moscow, citing developments in Russian airspace.

Ukrainian presidential spokesman Andriy Yermak has said Russia must be held responsible for the crash.

The Kremlin has refused to comment on reports that the Azerbaijan Airlines plane was hit by Russian air defence.

"An investigation into this aviation incident is underway and until the conclusions are made as a result of the investigation, we do not consider ourselves entitled to give any assessments," said spokesman Dmitry Peskov.

Vigils have been held in Azerbaijan to honour the pilots, who are credited with saving lives by managing to land part of the plane, despite themselves being killed in the crash.

Kazakh authorities have been treating the injured and working closely with Azerbaijan on the investigation. However, they have refused to give details of their crash investigation.

Reports in Baku suggest both Russia and Kazakhstan proposed having a committee from the Commonwealth of Independent States (CIS) - a regional organisation dominated by Russia - investigate the crash, but Azerbaijan had instead demanded an international inquiry rather than one involving former Soviet countries.