An Aseman Airlines ATR-72, a twin-engine turboprop used for short-distance regional flying, went down near its destination of the southern Iranian city of Yasuj, some 780 kilometers (485 miles) south of the Iranian capital, Tehran.

Aseman Airlines spokesman Mohammad Taghi Tabatabai told state TV that all on Flight No. 3704 were killed. The plane carried 60 passengers, including one child, and six crew members.

Due to foggy condition, rescue helicopters couldn’t 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.

Aseman Airlines, owned by Iran’s civil service pension foundation, is a semi-private air carrier headquartered in Tehran that specializes in flights to remote airfields across the country. It also flies internationally.

The carrier has a fleet of 29 aircraft, including six ATR aircraft, according to FlightRadar24, a plane-tracking website. It is Iran’s third-largest airline by fleet size, behind state carrier Iran Air and Mahan Air.

The Iranian Red Crescent said it has deployed to the area. Authorities said they would be investigating. Locals described hearing the crash, though no one had found the crash site yet, according to state TV.

European airplane manufacturer ATR, a Toulouse, France-based partnership of Airbus and Italy’s Leonardo SpA., said it had no immediate information about the crash. The manufacturer specializes in regional turboprop aircraft of 90 seats or less.

Under decades of international sanctions, Iran’s commercial passenger aircraft fleet has aged, with air accidents occurring regularly in recent years.

Following the 2015 landmark nuclear deal with world powers, Iran signed deals with both Airbus and Boeing to buy scores of passenger planes worth tens of billions of dollars. US politicians have expressed concern about the airplane sales to Iran. President Donald Trump remains skeptical of the atomic accord overall and has refused to re-certify it, putting the deal in question.

Home to 80 million people, Iran represents one of the last untapped aviation markets in the world. However, Western analysts are skeptical that there is demand for so many jets or available financing for deals worth billions of dollars.

In April 2017, ATR sealed a $536-million sale with Iran Air for at least 20 aircraft. Chicago-based Boeing also signed a $3 billion deal that month to sell 30 737 MAX aircraft to Aseman Airlines.