An Iranian ATR 72, operated by Aseman Airlines, has crashed into mountains near the town of Semirom in Isfahan province.
The aircraft, which was carrying 66 people, is believed to have hit Mount Dena near Kahangan village in Padena District.
Leader of the Islamic Revolution Ayatollah Seyyed Ali Khamenei and President Hassan Rouhani have offered condolences to the bereaved.
Russian President Vladimir Putin also expressed grief for the victims of the “tragedy.”
The German government also expressed sorrow over crash of the Iranian passenger plane, with Chancellor Angela Merkel's spokesman saying in a tweet on Sunday that the crash was "terrible news."
Das ist eine schreckliche Nachricht vom Flugzeugabsturz in den iranischen Bergen. Wir nehmen Anteil an der Trauer des iranischen Volks um die Menschen, die dabei ihr Leben verloren haben.
— Steffen Seibert (@RegSprecher) February 18, 2018
Steffen Seibert said the German government "shares the grief of the Iranian people for those who lost their lives."
16:02 pm (1232 GMT): Iranian Minister of Roads and Urban Development Abbas Akhondi says Tehran has contacted ATR to send a representative for further investigation. The wreckage has yet to be found but a team of 70 specialized mountain climbers are dispatched to carry on the search operations.
15:35 pm (1205 GMT): Head of Judiciary Ayatollah Bagher Amoli Larijani issues statement, urging the Attorney General to tasking a committee with identifying those responsible for the deadly crash.
14:20 pm (1050 GMT): Smoke is seen bellowing from Padena, southeastern Isfahan. Local rescue teams are investigating the source.
13:40 pm (1010 GMT): Head of Red Crescent teams at the site says drones are being flown over the perimeters.
13:28 pm (0958 GMT): So far 20 rescue teams from nearby cities have been dispatched to area.
12:25 pm (0855 GMT): Investigative teams have not spotted any wreckage at the Kohandan-Bideh region. Bad weather is keeping surveillance and rescue choppers from flying. Head of Isfahan’s Red Crescent says they need at least two more hours to locate the crash site.
12:20 pm (0850 GMT): Heavy rain and fog is hurdling rescue efforts.
11:58 am (0828 GMT): The turboprop ATR 72 is a short-range aircraft made by the Italian-French company ATR. The one that crashed today is said to be a 1993 model that had been grounded for seven years until recently.
11:55 am (0825 GMT): The wreckage has yet to be spotted. Rescue teams are an estimated 50 kilometers away.
11:52 am (0822 GMT): The flight crew are identified as:
11:50 am (0820 GMT): Head of Iran’s Emergency Care Service (EMS): Rescue helicopters are coming back to their bases and will fly in better weather conditions. Ground search and rescue missions are on their way.
11:46 am (0816 GMT): All passengers are believed dead, officials say.
11:45 am (0815 GMT): Besides 60 passengers, including a child, there were 2 pilots and 2 stewards on board the flight.
11:42 am (0812 GMT): Up to 5 helicopters are flown to find the wreckage. The mountainous terrain makes it impossible for rescue vehicles to reach the area.
11:30 am (0800 GMT): Aseman airlines official confirms the crash and says the flight has hit the Dena heights, within the Zagros Mountains.
10:43 am (0713): The airplane has disappeared from radars, Aseman Airlines says.
Air controllers said the plane went off radar screens 50 minutes after take-off from Mehrabad airport in Tehran at around 8:00 am (0430 GMT). The flight had 60 passengers, including a child, and six crew.
The Islamic Republic of Iran Broadcasting (IRIB) said the plane crashed around 23 kilometers (14 miles) from Yasuj, some 500 kilometers south of the capital.
Franco-Italian planemaker ATR has a deal with flag carrier Iran Air for the delivery of 20 ATR 72-600 passenger planes. The company delivered eight aircraft in 2017 and plans to deliver a further 12 by the end of this year.
The 70-seat ATR planes are aimed at domestic routes, which Iran seeks to revitalize after the lifting of sanctions in early 2016.