Iranian rescue teams resumed their search on Monday for a passenger plane that disappeared high in the Zagros mountains the previous day with 66 people onboard, local media reported.
State television said the weather had improved after blizzard conditions hampered search efforts Sunday, and that helicopters were now able to take part in the hunt for Aseman Airlines flight EP3704.
The authorities had called off the rescue effort overnight as heavy snow and rain made it impossible to work.
The ATR-72 twin-engine plane, in service for 25 years, left the capital's Mehrabad airport at around 8:00 am (0430 GMT) on Sunday and was heading towards the city of Yasuj, some 500 kilometres (300 miles) to the south.
It is thought to have crashed on the Dena mountain of Iran's southwestern Zagros range, but one official said there could be as many as 100 peaks to search in the vast and remote area.
"The visibility in the defined search area is not very good and there is turbulence, so these safety concerns must be taken into account," Morteza Dehghan of the Civil Aviation Organisation told state television.
"Despite all these conditions, both land and air teams are active. As soon as permission is given, drones will be used as well."
Around 100 mountaineer rescue workers were deployed on Monday, state television said.
France's air safety agency BEA said it would take part in the investigation led by Britain's Air Accidents Investigation Branch.
"Three investigators and our technical advisers will go to the site," a BEA spokesman told AFP.