By Nathan Morley
The wreckage of the Aseman Airlines plane is thought to be in the Zagros Mountains, but blizzard like conditions have hindered efforts to pinpoint the exact site of the tragedy.
The domestic flight vanished from radars an hour after leaving Tehran Airport for city of Yasuj on Sunday.
Twenty emergency teams continue scouring the region, with the Civil Aviation Organization of Iran announcing that 66 people - all passengers and crew on the ill-fated flight were killed.
There is no immediate indication of the cause of the crash, but officials from the department of aviation will examine the black box of the ATR-72 once it is discovered.
According to media in Iran, the aircraft had been in service for 25 years.
Iran's President Hassan Rouhani spoke of his "great grief and sorrow" and sent his sympathy to the families of those lost in the disaster.
Relatives of the plane's passengers have gathered at Tehran airport and Yasuj, its intended destination.
Aseman Airlines is a large company with a fleet of 26 planes.