The US National Transportation Safety Board (NTSB) will join the probe into the crash of the Ukrainian passenger plane.
In a statement posted on its Twitter account, the agency said it had received formal notification of the crash from Iran.
The US-made Boeing 737, operated by Ukraine International Airlines went down shortly after takeoff from Tehran airport in the early hours of Wednesday.
Canada, which had dozens of passengers on board, has also appointed an expert, while a team from Ukraine has already held discussions in Tehran.
Canadian Prime Minister Justin Trudeau said earlier the jet might have been brought down by an accidental Iranian missile strike, citing intelligence sources.
US targets three Iranian oil vessels after attack on Navy ships
Four killed in Israeli strikes on southern Lebanon
Indonesia's Anak Krakatau eruption halts flights, schools, fishing
Putin says US-Russia contacts beneficial as talks begin with Witkoff and Kushner
Chinese national rescued from Nepal tunnel 10 days after flash flood
