All passengers and crew aboard the plane have died.
The Ukraine International Airlines flight was bound for the Ukrainian capital of Kiev.
There is now evidence to suggest an Iranian missile brought down the plane, possibly in error.
Iranian officials initially blamed “technical issues” before saying the crash was most likely caused by an engine fire.
The Ukrainian embassy in Tehran ruled out terrorism but then amended its statement to offer no comment on the cause.
According to flight-tracking websites, the plane crashed about eight minutes after taking off from Imam Khomeini International Airport.
It comes just hours after Iran fired ballistic missiles into US airbases in Iraq.
The plane believed to have crashed is a Boeing 737-800, part of a previous generation of the 737 family.
It is not part of the 737 Max generation, which has been grounded worldwide since early 2019 following two of the planes crashing within five months.
We are following reports that a Ukrainian 737-800 has crashed shortly after takeoff from Tehran. #PS752 departed Tehran at 02:42UTC. Last ADS-B data received at 02:44UTC. https://t.co/qXWHUPGDTu pic.twitter.com/vuAi6TOqTp
— Flightradar24 (@flightradar24) January 8, 2020
