A passenger plane flying from Tehran and carrying 66 people crashed on Sunday in the Zagros Mountains, with authorities unable to confirm a death toll.
The Aseman Airlines flight disappeared from radar 45 minutes after departing the Iranian capital for the city of Yasouj in southwestern Iran. It came down near the city of Semiron in Isfahan province.
Conflicting reports emerged on the number of fatalities and location of the crash as emergency workers were unable to find the wreckage due to severe weather conditions.
The airline initially announced that all 66 passengers on board had been killed.
“After searching the area, we learnt that unfortunately our dear passengers had lost their lives,” said Aseman Airlines spokesperson Mohammad Taghi Tabatabai.
The airline later retracted this statement, however, saying: "Given the special circumstances of the region, we still have no access to the spot of the crash and therefore we cannot accurately and definitely confirm the death of all passengers of this plane."
Mr Tabatabai said the flight had been carrying 60 passengers, two security guards, two flight attendants and a pilot and co-pilot.
Iranian President Hassan Rouhani ordered the transport ministry to set up a crisis group to investigate the crash and co-ordinate rescue efforts, the semi-official ISNA news agency reported.
The regional head for Iran's emergency services, Jalal Pooranfar, said emergency workers were struggling to locate the wreckage in blizzard conditions.
"The helicopter could not continue its path due to snow and blizzard," Mr Pooranfar said, adding that emergency workers had been sent to the possible area of the accident.
The Iranian Red Crescent also said it had sent emergency teams to the area.
The head of the Red Crescent's local office, Seyed Noor Moahmmad Mousavi, said a drone had been dispatched to help find the wreckage.
A total of 120 people from 30 different emergency teams had been sent to help with the search, another Red Crescent official said.
Germany expressed sorrow over the accident, with Chancellor Angela Merkel's spokesman tweeting that the crash was "terrible news".
Iran has suffered multiple aviation disasters, most recently in 2014 when a Sepahan Airlines plane crashed just after take-off from Tehran, killing 39 people. That plane plummeted close to a busy market, narrowly avoiding many more deaths.
Lifting sanctions on aviation sales was a key clause in the nuclear deal that Iran signed with world powers in 2015.
Following the deal, Aseman Airlines finalised an agreement to buy 30 Boeing 737 MAX jets for $3 billion last June, with an option to buy 30 more. However, if US president Donald Trump decides to reimpose sanctions in the coming months, as he had threatened to do, the sale could be scrapped.
Owned by Iran's civil service pension foundation, Aseman Airlines is a semi-private air carrier headquartered in Tehran that specialises in flights to remote airfields across the country. It is Iran's third-largest airline by fleet size, behind state carrier Iran Air and Mahan Air.
Aseman Airlines also operates internationally but is banned from flying in the European Union over safety concerns.