* Ukraine, engine maker say too soon to speculate over cause
* Dead include 82 Iranians, 63 Canadians
* Plane was Boeing 737-800
* Unverified video purports to show plane on fire in sky 

A Ukrainian airliner crashed shortly after take-off from Tehran on Wednesday, bursting into flames and killing all 176 people on board.
Debris and smouldering engine parts from the Boeing 737, which carrier Ukraine International Airlines said was last serviced two days ago, were strewn across a field southwest of the Iranian capital where rescue workers in face masks laid out scores of body bags.
Among the victims were 82 Iranians, 63 Canadians, 11 Ukrainians, 10 Swedes, three Germans and three Britons, Ukrainian Foreign Minister Vadym Prystaiko said. Most passengers were in transit, the airline said.
The plane crashed hours after Iran launched missiles at bases housing US forces in Iraq, with the confrontation between Tehran and Washington threatening to cause a wider conflict in the Middle East. Officials cautioned that speculation about what happened was premature.

People and rescue teams are pictured amid bodies and debris. AFP

Passengers' belongings are seen at the crash site. Reuters

One of the engines of the crashed aircraft seen among the debris
. Reuters

It was the Kiev-based carrier's first fatal crash, and it said it was doing everything possible to establish the cause.
Ukraine will send a team of experts to Iran later on Wednesday to investigate the crash, President Volodymyr Zelenskiy said in the Ukrainian capital.
"Our priority is to establish the truth and those responsible for this terrible catastrophe," he said.
Canadian Foreign Minister Francois-Philippe Champagne said he was in touch with Ukraine's government.
"Our hearts are with the loved ones of the victims ... We will continue to keep Canadians informed as the situation evolves," he said on Twitter.
Under international rules, responsibility for investigating the crash lies with Iran, and Iranian state television said both of the plane's black box voice and data recorders had been found.
The semi-official Mehr news agency quoted the head of Iran's civil aviation organisation as saying it was not clear which country Iran would send the black boxes to for analysis of the data, but it would not give them to Boeing.
An amateur video, run by Iranian news agencies and purportedly of the crashing plane, showed a flash in a dark sky descending. It was accompanied by comments that the aircraft was "on fire" and then a brighter flash as it appears to hit the ground. Reuters could not authenticate the footage.
Asked at a briefing in Kiev if the plane could have been hit by a missile, Ukraine's Prime Minister Oleksiy Honcharuk cautioned against speculation until the results of the investigation were known.
Iran had earlier fired missiles at bases housing US forces in Iraq in retaliation for a US drone strike last week that killed an Iranian military commander.
Some airlines cancelled Iran and Iraq flights and re-routed others away from both countries' airspace following the missile strikes.
Safety experts say airliner accidents rarely have a single cause and that it typically takes months of investigation to understand all the factors behind them.
In Paris, the maker of the plane's engines, French-US firm CFM - co-owned by General Electric and France’s Safran - said speculation regarding the cause was premature.
Iranian TV put the crash down to unspecified technical problems, and Iranian media quoted a local aviation official as saying the pilot did not declare an emergency.
An official at Ukraine's embassy in Tehran said Iranian authorities had asked it to rescind an initial statement from Iran based on preliminary information that had blamed the accident on engine failure.
The plane that crashed was a three-year-old Boeing 737-800NG en route to Kiev. Its last scheduled maintenance was on Jan. 6, the airline said.
"We are in contact with our airline customer and stand by them in this difficult time. We are ready to assist in any way needed," the manufacturer said in a statement.
The 737-800 is one of the world’s most-flown models with a good safety record and does not have the software feature implicated in crashes of the 737 MAX. Boeing grounded its 737 MAX fleet in March after two crashes that killed 346 people.
Modern aircraft are designed and certified to cope with an engine failure shortly after take-off and to fly for extended periods on one engine. But an uncontained engine failure releasing shrapnel can cause damage to other aircraft systems.
Zelenskiy said he had instructed Ukraine's prosecutor general to open criminal proceedings, without specifying who they would involve.
Under international rules, Ukraine would be party to the investigation, and the United States would usually be accredited as the country where the jet was designed and built. France, where engine maker CFM has half its activities, may also be involved.
There was no immediate word on whether the US National Transportation Safety Board would be involved. The NTSB usually invites Boeing to give technical advice in such investigations.
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