Aseman Airlines Flight 3704 was flying from Tehran's Mehrabad International Airport to the southern city of Yasuj and crashed in the vicinity of the 14,000-foot Dena mountains, airline officials said.
The ATR-72, a twin-engine turboprop aircraft used for short distances, went down about 50 minutes into the 350-mile journey, said a spokesman for the airline, Mohammad Taghi Tabatabaei.
Officials earlier said 66 people were aboard the plane, but the state-run IRNA news agency reported later that one person listed as a passenger had missed the flight. There were 59 passengers and six crew members on the flight, the news agency said.
The cause of the crash was not immediately known, although airline officials blamed bad weather in the mountains.
Rescue workers also said they were having difficulty landing air ambulances near the crash site due to heavy fog.