* 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 (Adds Pompeo, bridal party)
DUBAI/KIEV, Jan 8 (Reuters) - A Ukrainian airliner crashed shortly after take-off from Tehran on Wednesday, bursting into flames and killing all 176 people on board.
The Boeing 737 crashed hours after Iran fired missiles at bases housing U.S. forces in Iraq, and officials said speculation about what happened was premature. Carrier Ukraine International Airlines said the plane was last serviced two days ago.
Smouldering parts and debris, including shoes and clothes, 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.
A passenger list https://www.flyuia.com/ua/ua/news/2020/flight-ps752-passenger-list from the airline showed members of the same family were killed, children were on board and many passengers were under 35. A newlywed couple that had gone to Iran to get married were among the Canadian victims.
Arash Pourzarabi, 26, and Pouneh Gourji, 25, were graduate students in computer science at the University of Alberta. Four members of their wedding party were also on board with another 24 Iranian-Canadians from Edmonton, said Reza Akbari, president of the city's the Iranian Heritage Society.
"Oh god, I cant believe this," Akbari told Reuters. "Its shocking to the whole community."
Canadian Prime Minister Justin Trudeau said he was "shocked and saddened" and added: "Our government will continue to work closely with its international partners to ensure that this crash is thoroughly investigated, and that Canadians questions are answered."
It was Kiev-based Ukraine International Airlines' first fatal crash, and the carrier 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. He said he had instructed Ukraine's prosecutor general to open criminal proceedings.
U.S. Secretary of State Mike Pompeo said the United States was calling for complete cooperation with any investigation into cause of the crash and was prepared to offer Ukraine all possible assistance.
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.
Iran had earlier fired missiles at the bases housing U.S. forces in Iraq in retaliation for a U.S. 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-U.S. firm CFM - co-owned by General Electric and Frances 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 worlds 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.
The U.S. National Transportation Safety Board said it was monitoring developments surrounding the crash.
(Reporting by David Shepardson in Las Vegas and Allison Lampert in Montreal; Editing by Raju Gopalakrishnan, Simon Cameron-Moore, Giles Elgood and Timothy Heritage)