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A Ukrainian Boeing 737-800 with 176 people on board has crashed in Iran, and officials say there is no chance of finding survivors.

Ukraine International Airlines flight PS752 to Kyiv went down just minutes after taking off from Tehran's airport at 06:12 local time (02:42 GMT).

The majority of passengers were from Iran and Canada.

Ukraine's Tehran embassy initially blamed engine failure but later removed the statement.

It said any comment regarding the cause of Wednesday's accident prior to a commission's inquiry was not official.

• Who are the victims of the crash?

There was good visibility when the plane went down near Iran's capital, according to the Flightradar24 aviation website. Officials from the airline said the crew were experienced.

Ukraine International Airlines (UIA) said the Boeing 737-800 was built in 2016 and had its last scheduled maintenance on Monday.

Hours before the plane came down Iran carried out a ballistic missile attack on two air bases housing US forces in Iraq. There is no evidence that the two incidents were linked.

Ukraine's president, Volodymyr Zelensky, warned against "speculation or unchecked theories regarding the catastrophe" until official reports were ready.

What are Iranian authorities saying?

Iranian media blamed technical problems and quoted an aviation official who said no emergency had been declared.

In a sign of the potential difficulties facing crash investigators, the head of Iran's civil aviation organisation was quoted as saying the Ukrainian plane's "black boxes" - the cockpit voice recorder and the flight data recorder - had been found but would not be handed over, either to Boeing or the Americans.

Ali Abedzadeh said "terrorism" had played no role in the crash, Iran's conservative Mehr news agency reported. He added that at this stage it was unclear who would analyse the black boxes.

Another Iranian official, Qasem Biniaz, blamed an engine fire. "Had the accident happened due to a missile strike, the plane would have exploded in the air," he told the IRNA news agency.

Normally, the US National Transportation Safety Board would have a role to play in any international investigations involving US-made Boeings. But the board must act with permission and in accordance with legislation of the foreign country concerned.

Video circulating on social media appeared to show the last few seconds of the plane's flight. It can be seen streaking across the night sky while on fire before it quickly loses height. There is an initial explosion close to the ground and then a final blast that lights up the area.

Debris and engine parts from the Boeing 737-800 NG plane were found some 10km (6 miles) from Tehran's Imam Khomeini airport to the west of the capital, and rescue workers with face masks searched the wreckage for victims.

Throughout the morning, Red Crescent workers laid out a long line of body bags. Personal effects such as children's books, clothes and shoes lay strewn around the area, alongside the mangled debris of the plane.

The head of Red Crescent said that it was "impossible" for anyone to have survived the crash.

All direct flights between Ukraine and Iran were suspended, while a number of airlines announced that they were avoiding both Iranian and Iraqi airspace.

Air France and KLM said they would use alternative routes while Lufthansa said it was also cancelling its daily flight to Tehran. Qantas, Air India, Japan Airlines, Singapore Airlines and Malaysia Airlines were among other airlines taking action.

Who was on board?

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

• Three British nationals among dead in plane crash

Ukrainian officials said that 169 people had bought tickets for the flight but two had not boarded the plane.

The German government later said "we currently have no knowledge that German citizens are among the victims of the plane crash in Iran".

It was unclear why such a large number of Canadians were on board, however the airline provides relatively inexpensive flights via Kyiv to Toronto. Some of the Canadians were thought to be students returning at the end of the school holidays.

Prime Minister Justin Trudeau said he was "shocked and saddened" by the news of the crash, offering "deepest condolences to those who have lost family, friends, and loved ones in this tragedy".