Ukraine's embassy in Tehran said engine failure caused the crash and there was no link to terrorism.

"According to preliminary information, the plane crashed as a result of an engine failure for technical reasons. Currently, the version of a terrorist attack is ruled out," the embassy said on the Ukraine Foreign Ministry's website.

Among the victims were 82 Iranians, 63 Canadians, 11 Ukrainians including all the crew, 10 Swedes, four Afghans, three Britons and three Germans, Foreign Minister Vadym Prystaiko said.

Ukraine's President Volodymyr Zelensky said he was cutting short a trip to Oman and flying back to Kyiv. He warned against "speculation or unchecked theories regarding the catastrophe" until official reports were ready.

"My sincere condolences to the relatives and friends of all passengers and crew," he said in a statement.

Rescue teams have been sent to the crash site but the head of Iran's Red Crescent told state media that it was "impossible" for anyone to have survived the crash.

Rescue workers had found one of the airliner's black boxes, Iranian media reported.

Aviation safety analyst Todd Curtis told the BBC that the aircraft involved in the crash had been manufactured in 2016 and delivered new to the airline.

"The airplane was heavily fragmented which means either there was an intense impact on the ground or something happened in the sky," he said.

"From all appearances this was an airplane that had been properly cared for and there were no outstanding issues with respect to European authorities or American authorities so at this point there is nothing that points to a particular cause."

Mr Curtis said Iranian, Ukrainian, US and French authorities would all be involved in the investigation, but it was unclear how they would work together. Iran is currently under US sanctions and there are severe tensions between the two countries.

"They will start putting together the story of what happened on that airplane... to see if there is something about the condition of the aircraft or the fuel on board that might have led to this," he said.

"And also one cannot discount the possibility that something outside the aircraft, a mid-air collision or some other issue, may have been involved."