The announcement by Iran’s Civil Aviation Organisation head, Ali Abedzadeh, follows the launch of an urgent inquiry into the crash by the Ukrainian government, which itself rowed back on an earlier statement ruling out an act of terror.

Announcing on his Facebook page that Ukraine would send a team of experts to Iran later on Wednesday, the country’s president, Volodymyr Zelenskiy, said: “Our priority is to establish the truth and those responsible for this terrible catastrophe.”

The developments have fuelled uncertainty around the circumstances of the crash, which came only hours after Iran had fired a volley of intermediate range ballistic missiles at bases used by US forces in neighbouring Iraq in relation for America’s assassination of the powerful Iranian general Qassem Suleimani in Baghdad on Friday.

Commenting after the discovery of the black box flight recorders at the crash site, Abedzadeh said: “We will not give the black boxes to the manufacturer (Boeing) and the Americans. It’s not yet clear which country the black box will go to for the investigation,” he added.

“This accident will be investigated by Iran’s aviation organisation but the Ukrainians can also be present during the incident’s investigation,” he added.

Journalists from Associated Press, who reached the crash site on Wednesday morning, described farmland covered with debris. The dead lay among shattered pieces of the aircraft, their possessions, including a child’s electric toothbrush, a stuffed animal, luggage and electronics, strewn across the site.

Iran’s insistence that it will not hand over the black boxes to Boeing comes amid claims that at least two aircraft which had been originally routed through Iranian airspace around the time of the Iranian missile attacks on the bases in Iraq were either told to turn around or redirected.

Ukraine’s foreign minister, Vadym Prystaiko, said that there were 82 Iranians, 63 Canadians and 11 Ukrainians on board. The Ukrainian nationals included two passengers and the nine crew. There were also 10 Swedish passengers, four Afghans, three Germans and three British nationals, he said.

The Ukraine International Airlines flight PS752 disappeared from flight trackers a few minutes after its delayed take off from Tehran, apparently suffering a catastrophic incident that caused it to break up in flames over farmland outside the city with crew unable to issue a mayday alert.

Amateur video, allegedly showing the plane’s final moments, appeared to show a brightly burning object in the sky, breaking into pieces before exploding in orange flames on the horizon.

The video was published in the same website of the state-run Iranian Students News Agency, which also carried a photograph of section of wing from the crashed aircraft, which some analysts said appeared to show penetration damage to the aircraft.

Ukraine International Airlines said it had indefinitely suspended flights to Tehran after the crash, amid announcements from a slew of other international airlines that they would be avoiding Iranian and Iraqi airspace following the escalating tensions between the US and Iran.

“It was one of the best planes we had, with an amazing, reliable crew,” Yevheniy Dykhne, the president of Ukraine International Airlines, said at a briefing following the crash.

As the investigation got under way the aviation safety information-sharing website OpsGroup, which was set up following the shooting down of Malaysian airlines flight MH17 over Ukraine in 2014, urged airline operators to err on the side of caution until the cause of the crash had been established and work on the assumption the plane had been shot down.

Under the rules of the International Civil Aviation Organisation, of which Iran, Ukraine and the United States are all members, air crash investigations are led by the country where the accident occurred.

Iranian officials said they suspected a mechanical issue brought down the three-and-a-half-year-old Boeing 737-800 aircraft, an assessment Ukrainian officials initially agreed with but later backed away from offering a cause while the investigation is ongoing.

Amid speculation into the cause of the crash, the third in recent months involving a Boeing passenger aircraft, civil aviation insiders also pointed to the large debris field to suggest the plane had broken up suddenly in mid air.

The 737-800 belongs to the same family as, but is different to, the 737 Max 8 aircraft, which has been grounded since two fatal crashes occurred within six months in Indonesia and Ethiopia in 2018.

The 737-800 operates with a different software system to the one implicated in the Max 8 crashes.

The plane had been last serviced two days before the accident, according to the airline.

An investigation team was deployed to the site of the crash on the south-western outskirts of Tehran on Wednesday morning, said Reza Jafarzadeh, a civil aviation spokesman. Qassem Biniaz, a spokesman for Iran’s road and transportation ministry, told the state-run Irna news agency it appeared the pilot had lost control after a fire struck one of the plane’s engines.

Hassan Rezaeifar, the head of the air crash investigation committee, said it appeared the pilot could not communicate with air-traffic controllers in Tehran in the last moments of the flight. He did not provide further details.

Zelenskiy, who cut short a visit to Oman following the crash, ordered an investigation and a sweeping check of “all civilian aircraft” in the country.

“Our task is to establish the cause of the crash of the Boeing and provide all necessary help to the families of the victims,” Dmytro Razumkov, the speaker of the Ukrainian parliament, said in a statement on Facebook.

The UK Foreign Office added it was urgently seeking confirmation about how many British nationals were onboard, and that it would do all it could to support any families affected.

One witness, Aref Geravand, told AP the pilot managed to steer the plane towards a football field and away from a residential area, saying: “It crashed near the field and in a water canal.”

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