"We will not give the black boxes to the manufacturer (Boeing) and the Americans," Iran Civil Aviation Organisation head Ali Abedzadeh said, quoted by Mehr news agency.
"It's not yet clear which country the black box will go to for the investigation," he added.
Following the crash of Ukraine International Airlines flight PS752 shortly after takeoff from Tehran on Wednesday, Iran said it had recovered the Boeing 737's two black boxes.
Ukrainian airliner crashes after take-off in Iran, killing all 176 aboard
Abedzadeh said that based on global aviation rules, it was the right of the country where air crashes occur to carry out the investigation.
"This accident will be investigated by Iran's aviation organisation but the Ukrainians can also be present during the incident's investigation," he added.
Under the rules of the International Civil Aviation Organisation, of which Iran, Ukraine and the United States are all members, air crash investigations are led by the country where the accident occurred.
However, according to aviation experts, the countries that are capable of analysing black boxes are few, notably Britain, France, Germany and the United States.
France's Accident Investigation Bureau (BEA), which handles air crash investigations, said it had not received any request for help from the Iranian authorities after Wednesday's crash.
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