A Ukrainian Boeing 737-800 airliner carrying at least 176 people crashed shortly after takeoff from Tehran on Wednesday, killing everyone on board.
It was unclear what caused the crash of the aircraft, a Ukraine International Airlines flight bound for Kyiv, the Ukrainian capital. Early statements from both countries were confused and contradictory.
The disaster happened against the backdrop of the escalating tensions between the United States and Iran, which on Tuesday fired missiles at two bases in Iraq that house American troops, but there was no immediate indication that the plane had been shot down or otherwise attacked.
The Iranian Students’ News Agency, a state-run media organization, shared a video it said showed the predawn crash, with an aircraft, apparently in flames, descending in the distance before a bright burst filled the sky upon impact.
Photos and videos from the crash site showed rescuers in a field littered with plane debris, smoldering fires and the belongings of passengers.
Qassem Biniaz, an official at the Iranian Ministry of Roads and Urban Development, told the Islamic Republic News Agency, the government’s official news agency, that an engine caught fire and the pilot was unable to regain control. Ukraine International Flight 752 left Imam Khomeini International Airport in Tehran at 6:12 a.m. on Wednesday and lost contact at 6:14 a.m., according to a flight tracker.
Iranian news organizations tied to the government referred to technical problems with the plane, but they did not elaborate or cite any evidence. Later, the head of Iran’s Civil Aviation Organization, Ali Abedzadeh, told the semiofficial Mehr News Agency that so far, there was no evidence of technical problems.
The disaster has the potential to add to the crisis at Boeing, which has been dealing with the fallout from two crashes involving a different model of jet.
After the crash, Ukraine’s Embassy in Iran initially issued a statement ruling out terrorism or a rocket attack as a cause of the crash. But the statement was later removed from the embassy’s website and replaced by a statement saying it was too early to draw any conclusions.
Mr. Abedzadeh said the airliner had not contacted the control tower about an emergency.
After an accident, the “black boxes” are often sent to the plane’s maker for analysis, but Iran would not send the flight data recorders to Boeing, an American company, Mr. Abedzadeh said in an interview with Mehr.
“We will not give the black box to the manufacturer and the Americans,” Mehr quoted him as saying. Ukrainian officials, he said, would be involved in Iran’s investigation of the crash.
There were 176 people aboard, including nine crew members, according to Ukrainian officials, but the Iranian authorities, who released the names of the dead, listed 177, while some Iranian news organizations cited other figures. The breakdown of the victims’ nationalities also diverged, though that may be because some passengers held dual citizenship; Iran’s tally included 147 Iranians and two Canadians, while Vadym Prystaiko, Ukraine’s minister of foreign affairs, said there were 82 Iranians and 63 Canadians.
At a news conference at Boryspil International Airport in Kyiv several hours after the crash, Ukraine International Airlines executives said the plane had been in good working order and operated by a highly trained crew. They offered no theories as to what might have happened and declined to comment on whether or not it might have been shot down.
“Given their experience, it is very difficult to say that there was something wrong with the crew,” Ihor Sosnovskyi, the airline’s vice president of flight operations, said at the briefing.
President Volodymyr Zelensky of Ukraine said he had ordered the prosecutor general to open a criminal investigation into the crash and that the country’s entire civil aviation fleet would be checked.
“All possible versions of what occurred must be examined,” Mr. Zelensky said in a Facebook post.
Boeing faces its own pressure. The company has been under intense scrutiny after the crash of two 737 Max jets in less than five months, which together killed 346 people. The Max has been grounded worldwide since March, creating a crisis for the company and leading to the firing of the chief executive.
As the company struggles to get a fix for the Max approved by regulators, new safety risks have recently emerged with the plane, which the company may also need to assess on the 737-NG family, which includes the 737-800. The 737-NG is one of the world’s most widely used airliners, with almost 5,000 built since 1998, and it generally has a good safety record.
“We are aware of the media reports out of Iran and we are gathering more information,” Boeing said in a statement.
The crash came at a tense time in Iran, as conflict with the United States had the country on edge. On Tuesday, the Federal Aviation Administration barred American airliners from flying over Iran, citing a risk that commercial planes would be mistaken for military aircraft. Several non-American carriers rerouted flights on Wednesday to avoid Iraq and Iran, according to Flightradar24, a site that tracks airplane transponders.
In 2014, early in the war in eastern Ukraine between government forces and Russia-backed separatists, a Russian missile shot down Malaysia Airlines Flight 17, killing 298 people.
The crash could touch a nerve politically in Ukraine, because Ukraine International Airlines is partly owned through a network of offshore companies by Ihor Kolomoisky. Mr. Kolomoisky is an oligarch with close ties to the Ukrainian president.
Mr. Zelensky cut short his trip to Oman, where he was spending the holidays, and was returning to Kyiv. “Horrible news from the Middle East,” he said in a post on Facebook. “My sincere condolences to the relatives and loved ones of all of the passengers and crew members.”
While airlines in the former Soviet Union have a generally poor safety record, Ukraine International Airlines says on its website that its safety is audited and meets Federal Aviation Administration standards for code-sharing flights with foreign partners. It had not previously suffered a fatal crash, according to a list of Ukrainian aircraft accidents compiled by the Flight Safety Foundation.
The airline said the plane was manufactured in 2016 and delivered directly from the factory, and that it had most recently undergone scheduled maintenance on Monday — two days before the crash. The airline said it was canceling flights to Tehran indefinitely and promised a full investigation into the causes of the crash, involving officials from Ukraine, Iran and Boeing.
The airline began in the 1990s as newly independent Ukraine’s state flag carrier but was subsequently privatized. Its website calls the business a “public private entity.” Before suspending service to Tehran on Wednesday, the carrier offered five direct flights per week from the Iranian capital to Kyiv. The airline flies a fleet of 35 Boeings and seven Embraer aircraft, according to its website.
Officials from the Ukrainian Embassy in Tehran were at the airport Wednesday morning and working to compile a list of the passengers on board, Russia’s state-run RIA Novosti news agency cited an embassy official as saying. Ukraine’s Foreign Ministry said it had set up a crisis working group and a telephone hotline in response to the crash.
Daniel Victor reported from Hong Kong, and Anton Troianovski and Andrew Kramer from Moscow. Farnaz Fassihi contributed reporting from New York.