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.
Russian ballistic missiles kill 12 in Ukraine's Kyiv
Prince Harry and Meghan to move back to Britain
North Korea fires suspected ballistic missile, Japanese authorities say
Kenya tourist helicopter crash kills seven
US, South Korea to cut length, scope of military drills after Trump order
