"The plane crash has killed 72 people and injured 33," Fars news agency reported, quoting the coroner's office of West Azerbaijan province where the plane came down.
Earlier, state news agency IRNA reported that 70 people had been killed in the accident near the city of Orumiyeh.
"Based on information received so far, 70 people have been killed and 32 injured" in the crash, Heydar Heydari, deputy head of the Iranian Red Crescent, told state news agency IRNA.
The Mehr news agency, quoting a senior medical official, also reported that 70 people were killed in the crash.
"The bodies of 70 victims... were transferred to the provincial coroner's office," the official said.
The plane with the Islamic republic's national carrier crashed near the northwestern city of Orumiyeh at around 7:45 pm (1615 GMT), an official in West Azerbaijan province said, quoted on state television's website.
"The airplane took off an hour later than scheduled time from Tehran towards Orumiyeh and because of bad weather conditions came down in a village area near Orumiyeh," the unidentified official said.
The governor-general of West Azerbaijan, Vahid Jalalzadeh, told state television that "all the bodies and the injured have been transferred to different hospitals in the city" of Orumiyeh.
Giving sketchy details of the crash, Jalalzadeh said the pilot had lost contact with the airport before the airliner disappeared off the radar.
"Then the plane crashed near the village and villagers told the authorities about the crash site. Some passengers were able to get out of the plane themselves, and villagers took several passengers to hospitals," he said.
Another Iranian Red Crescent official told state television that the plane hit the ground and broke into pieces. "Thankfully there was no fire," he said.
State television footage of the crash showed the airliner broken into three pieces which lay buried in thick snow.
Iran Air spokesman Shahrokh Noushabadi said "we are examining the reason for the crash, but bad weather appears to be the main cause."
An official with the transport ministry told state television that one of the aircraft's two black boxes had been recovered, and this would help determine the cause of the crash.
Fars said 105 people were believed to have been on board, and ISNA reported that the aircraft was a US-built Boeing 727. A third news agency, ILNA, gave a breakdown of 95 passengers and 10 crew members.
Masoumi said the rescue operation was being hampered by bad weather.
"The problem at the moment for rescue work is the heavy snow, which is around 70 centimetres (more than two feet) deep around the crash site," Fars quoted him as saying.
IRNA reported that bad weather around Orumiyeh had earlier led to the cancellation of two flights from Tehran on Sunday.
Iran, which has been under years of international sanctions, has suffered a number of aviation disasters over the past decade, several involving small companies using Russian crew or crews from former Soviet republics in Central Asia.
The country's civil and military fleet is made up of ancient aircraft in very poor condition because of their age and lack of maintenance.
In Iran's worst air accident, a plane carrying members of the elite Revolutionary Guards crashed in February 2003, killing 302 people on board.
In July 2009, a Soviet-designed Tupolev caught fire in mid-air and plunged flaming into farmland northeast of Tehran, killing all 168 people on board.
And in December 2005, a total of 108 people were killed when a Lockheed transport plane crashed into a high-rise housing block outside Tehran.
In November 2006, a military plane crashed on takeoff at Tehran's Mehrabad airport, killing all 39 people on board, including 30 members of the Revolutionary Guards.