All passengers on board an Iranian domestic flight were killed on Sunday when their aircraft crashed into the Zagros Mountains, officials said. The plane was carrying 60 passengers, including one child, as well as six crew, said Mohammad Tabatabai, director of public relations for the Aseman Airlines. "After searches in the area, unfortunately we were informed that the plane crashed. Unfortunately, all our dear ones lost their lives in this incident," he added. The Aseman Airlines flight left Tehrans Mehrabad airport around 0800 (0430 GMT) for the city of Yasuj in Isfahan province. Due to foggy condition, rescue helicopters could not reach the crash site in the Zagros Mountains, state TV reported. Tabatabai said the plane crashed into Mount Dena, which is about 440-meters (1,440-feet) tall. A helicopter sent by Irans national emergency services was unable to land at the site of the accident due to severe weather, its spokesman said. The Relief and Rescue Organization of Irans Red Crescent said it had dispatched 12 teams to the region. "Given the fact that the area is mountainous, it is not possible to send ambulances," Mojtaba Khaledi, spokesman for the national emergency services, told ISNA news agency. President Hassan Rouhani has since ordered that an investigation be opened in the crash. Decades of international sanctions have left Iran with an aging fleet of passenger planes which it has struggled to maintain and modernize. It has suffered multiple aviation disasters, most recently in 2014 when a Sepahan plane crashed killing 39 people. Tabatabai said the plane that crashed on Sunday was a twin-engine turboprop ATR-72. Aseman currently has a fleet of 36 planes -- half of them 105-seat Dutch Fokker 100s. Its three Boeing 727-200s are almost as old as the Islamic revolution, having made their first flights in 1980. Lifting sanctions on aviation purchases was a key clause in the nuclear deal Iran signed with world powers in 2015. Following the deal, Aseman Airlines finalized an agreement to buy 30 Boeing 737 MAX jets for $3 billion (2.4 billion euros) last June, with an option to buy 30 more. However, the sale could be scuppered if US President Donald Trump chooses to reimpose sanctions in the coming months, as he has threatened to do. The US has maintained its own sanctions on Iran, which block almost all trade with the country, but plane manufacturers were given a specific exemption under the nuclear deal. Boeing, which is also building 80 planes for national carrier Iran Air, faces heavy criticism from US lawmakers who say Iranian airlines have been used to ship weapons and troops to Syria and other conflict zones. The US Treasury Department approved the sale of the 80 Boeing jets as well as 100 Airbus planes to Iran Air. The first few Airbus jets have already arrived in Tehran.