According to Mehr information agency, five Russian aviation experts will arrive in Tehran to investigate the Tu-154 airline crash together with Iran's aviation organization, the press-secretary of the organization, Rza Jafarzadeh, said.
"Reasons for crashes can be varied. So it would be incompetent to voice any concrete reason at this early stage," he said.
The representative of Iran's ministry of transport and the head of the group, Ahmed Majidi, is investigating the reasons for the catastrophe.
According to him, the 'black box' flight recorder will be brought back to Russia, the country where the aircraft is produced, for decoding.
The passenger aircraft crashed near the Iranian city of Qazvin on July 15. The aircraft made Tehran-Yerevan flights. There were 168 people on board - 153 passengers, including two children, and 15 crew members. A national youth judo team, leaving to Yerevan for a competition, was on board.