All 60 passengers and six crew members of the plane were killed in the incident.
The wreckage was spotted by a helicopter on Tuesday morning.
"Deep and unsafe crevices in the area of the crash have made it impossible for helicopters to land", Ghafoor Rastinrooz, director of the regional medical center, told official news agency IRNA.
Helicopters are unable to land in the mountainous terrain, and the work to find bodies will have to be carried out on foot, an emergency service official said.
In a letter dated Feb 20 and addressed to Iran's President Rouhani, President Halimah said that she was "saddened" to learn about the "tragic crash".
The Aseman Airlines flight left Tehran's Mehrabad airport around 0800 (0430 GMT) for the city of Yasuj in Isfahan province, said Mohammad Tabatabai, director of public relations for the airline.
"Little by little they have reached the area and are collecting bodies", Shahin Fathi, from Iran's Red Crescent, told state TV.
The incident has reawakened concerns over aviation safety in Iran, which has been exacerbated by global sanctions over the years.
Iranian rescue teams find site, wreckage from plane crash
Tabatabai said the plane that crashed on Sunday was a twin-engine turboprop ATR-72.
It was one of only three airlines barred over safety concerns - the other 190 being blacklisted due to broader concerns over oversight in their respective countries.
Iran's state media say the Iranian passenger plane that crashed in the country's south went down in a foggy, mountainous region, killing all 66 passengers on board.
Mojtaba Khaledi, spokesman for the national emergency services, said that a helicopter had been sent to the area. The Islamic Republic was not allowed to purchase new Western planes and spare parts for about two decades.
A deal with world powers on Iran's nuclear program has lifted some of those sanctions, opening the way for Iranian airlines to update their creaking fleets.
The US has maintained its own sanctions on Iran, which block nearly all trade with the country, but plane manufacturers were given a specific exemption under the nuclear deal.
Aseman signed a deal in 2017 to buy at least 30 Boeing 737 MAX jets.