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.


Palestinian teen shot dead in Israeli West Bank raid, Wafa reports
Libya says 17 migrants perish at sea, nine missing feared dead
Israel begins intercepting Gaza aid ships far from shores, army radio says
Trump urges Iran to sign a deal and discusses prolonged blockade
Seven people die in hospital wall collapse in southern India