The plane was said to have crashed in Dena Mountain but one official said there could be 100 peaks to search.
Iranian rescue teams battled severe weather Monday as they searched for a passenger plane that disappeared high in the Zagros Mountains the previous day with 66 people on board.
Several helicopters that had deployed at dawn to hunt for Aseman Airlines flight EP3704 were forced to return to base, officials said.
"Unfortunately due to strong winds and fog reducing visibility, it was not possible for helicopters to continue their search," a Red Crescent official told the ISNA news agency.
"Teams are searching by foot and so far they have not found anything."
Officials said hundreds of mountaineers, dogs and drones were operating around the Dena Mountain at altitudes as high as 4,500 meters (15,000 feet).
The ATR-72 twin-engine plane, in service for 25 years, left the capital's Mehrabad airport at around 8:00 am (0430 GMT) Sunday and was heading towards the city of Yasuj, some 500 kilometers (300 miles) to the south.
Several relatives of passengers have travelled to the Dena mountain area where the plane is thought to have come down, local media said.
A team of crash investigators from French air safety agency BEA was set to arrive in Iran later on Monday.
"Three investigators and our technical advisers will go to the site," a BEA spokesman told AFP.
Iran has suffered multiple aviation disasters, most recently in 2014, when 39 people were killed as a Sepahan Airlines plane crashed just after take-off from Tehran, narrowly avoiding many more deaths when it plummeted near a busy market.
Following the deal, Aseman Airlines finalized an agreement to buy 30 Boeing 737 MAX jets for $3 billion (2.4 billion euros) last June, with an option to buy 30 more.
However, the sale could be scuppered if US President Donald Trump chooses to reimpose sanctions in the coming months, as he has threatened to do.
Source: News Agencies, Edited by website team