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.


Israel carries out rare airborne raid in Lebanon; 16 killed in strikes
US skips congressional review to approve arms sale to Israel
Flash floods in Nairobi kill 23, disrupt flights at major airport
Russia hits Ukraine with drones, missiles, kills at least 10 in Kharkiv
Partial resumption of air navigation in Qatar
Kuwait and Qatar thwart fresh wave of Iranian attacks
After a week of war, Trump demands Iran's 'unconditional surrender'
Ex-rapper's party set to sweep Nepal election
