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 jet. It also happened against the backdrop of the escalating tensions between the United States and Iran, which on Tuesday attacked two bases in Iraq that house American troops.

Photos and videos from the crash site showed rescuers in a field littered with plane debris, smoldering fires and the personal belongings of passengers. The Iranian Students’ News Agency, a state-run media organization, shared a video it said showed the predawn crash, with a distant light descending in the distance before a bright burst filled the sky upon impact.

The crash took place as Iran was likely bracing for retaliation to its missile attacks hours earlier against U.S. military bases in Iraq. But the Ukrainian Embassy in Tehran said the passenger plane was not shot down.

“According to preliminary information, the airplane crashed as a result of engine failure due to technical reasons,” the embassy said in a statement. “The possibility of a terrorist attack or a rocket attack can currently be ruled out.”

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 Airlines 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

“We are aware of the media reports out of Iran and we are gathering more information,” Boeing said in a statement.