TEHRAN, Iran — A commercial plane crashed on Sunday in a foggy, mountainous region of Iran, most likely killing all 66 people on board, the state news media reported.

The Iran Aseman Airlines plane went down near its destination, the city of Yasuj, about 485 miles south of the capital, Tehran.

Mohammad Taghi Tabatabai, a spokesman for Aseman Airlines, initially told state television that everyone aboard the ATR-72, a twin-engine turboprop used for short-distance regional flights, had been killed.

The airline later issued a statement saying it could not reach the crash site and could not “accurately and definitely confirm” everyone had died.

The plane was carrying 60 passengers, including one child, and six crew members, according to The Associated Press. The cause of the crash was not immediately clear.

The Iranian Red Crescent said it had sent people to the area, and the authorities said they would be investigating.

But fog prevented rescue helicopters from reaching the site in the Zagros Mountains, state TV reported. Mr. Tabatabai said the plane had crashed into Mount Dena, which has an elevation of about 14,500 feet.

News reports said the plane disappeared from radar screens 50 minutes after taking off from Mehrabad International Airport, in western Tehran, which mainly serves domestic flights but has some international routes.