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.


Bangladesh's first female prime minister Khaleda Zia dies at 80
Peace hopes dented as Russia says Ukraine tried to attack Putin residence
US strikes drug boat loading facility in Venezuela, Trump says
Thailand and Cambodia agree to 'consolidate ceasefire' in China talks
Three Turkish police, six ISIS members killed in clash
