Suspicions of foul play in the crash of a Ukrainian passenger jet minutes after takeoff from Tehran last night intensified on Wednesday as Iran refused to hand over the black boxes from the aircraft. All 176 people aboard the plane reportedly died in the crash.

Iranian state media reported on Wednesday that both black boxes were recovered from the crash site on the outskirts of Tehran. The plane departed for Kyiv at 6:10 a.m. local time (9:40 p.m. Eastern), just hours after Iran launched missiles at two military bases in Iraq. It crashed only a few minutes after it cleared the runway at Imam Khomeini International Airport, coming down in a fiery crash amid farmland near the city. Eyewitnesses said the pilot appeared to steer the burning plane into an empty field as it descended.

According to flight-tracking data, the plane never reached 8,000 feet in altitude.

Iranian officials claimed the crash was caused by an engine fire. Video footage recorded by observers on the ground appeared to show the plane on fire in midair:

✈️ — UPDATE: First footage of moment the Boeing 737 Ukrainian Airlines plane crashes with 180 passengers in the Iranian capital, Tehran — No word on casualties or confirmed reason for the crash. Plane crashed moments after takeoff pic.twitter.com/VTnEXmesTK — ®️BELAAZ (@TheBelaaz) January 8, 2020

Ukraine initially accepted this theory, but on Wednesday they adjusted their position and said it was too early to determine the cause. Ukrainian officials agreed to coordinate with the Iranians to investigate the crash.

The aircraft was a three-year-old Boeing 737-800 described by Ukraine International Airlines (UIA) as “one of the best planes we had,” with an “amazing, reliable crew.” According to a statement from the airline, the plane received scheduled maintenance on Monday. UIA officials told NBC News that the airline has never had a plane crash before.

The airline suspended all flights to Iran after the crash, while Ukrainian President Volodymyr Zelensky ordered an immediate inspection of all civilian aircraft. A number of other international airlines have also suspended service to Iran.

Iranian investigators said the pilot of the plane was unable to communicate with Tehran air traffic controllers in the final minutes before the crash, but they did not explain why not. On Wednesday morning, Iran’s civil aviation authority refused to give the black boxes to Boeing, which would normally analyze the data, or to any American agency.

Ukrainian President Zelensky cautioned against speculating on the cause of the crash until an investigation is completed, but naturally, Iran’s conduct is fueling theories that Iranian forces either deliberately or inadvertently shot down the aircraft, possibly in a panic response because they anticipated possible American retaliation for the Iranian missile attack on Iraq.

The official tally of crash victims from the Ukrainian government includes 82 Iranians, 63 Canadians, 11 Ukrainians, ten Swedes, four Afghans, three Germans, and three Britons. Many of them were students, and according to media accounts of debris at the crash site, some of them were children.

Iranian officials said 147 of the victims were Iranians, which would suggest many of them had dual citizenship. The BBC noted that Kyiv is a layover for many passengers leaving Iran on affordable UIA flights, with Toronto the ultimate destination for many because it has a large Iranian community.