Their report said witnesses saw the Ukrainian International Airlines (UIA) Boeing 737-800 on fire as it descended, eventually crashing south west of the Iranian capital killing all 176 people onboard.
Three Britons were killed in the disaster. They have been named in the national press as Mohammed Reza Kadkhoda Zadeh, Sam Zokaei, and Saeed Tahmasebi.
The report by Iran’s civil aviation organisation (CAOI), cited by Reuters, said the three-year-old aircraft, which had undergone scheduled maintenance on Monday (6 January), encountered a yet-unspecified technical problem shortly after taking off.
It also said there was no radio communication from the pilots before the crash and that the aircraft, which was heading to Kiev, disappeared from radar at 8,000 feet.
CAOI chief said after initially heading west, the aircraft turned right and was "headed back to the airport at the moment of the crash".
Both Ukraine and Iran have played down speculation the aircraft was struck by an Iranian missile after the country launched strikes on two Iraqi military bases hosting US personnel in retaliation for the US airstrike, which killed top Iranian general Qasem Soleimani on Friday (3 January).
