Iranian rescue teams battled weather and mountainous terrain Monday as they searched for the wreckage of a plane that crashed with 65 people on board.
The Aseman Airlines flight left Tehran Sunday morning for the city of Yasuj in Isfahan province, but went down in the Zagros mountains. Officials fear all those on board were killed.
The search effort was initially delayed due to dense fog, high winds and snow that made it impossible for helicopters to get close to the crash site. Conditions improved enough Monday for the helicopters to operate.
The United Nations said Secretary-General Antonio Guterres joined world leaders in expressing sorrow over the crash. The U.N. said Guterres "was deeply saddened to learn of the tragic airplane accident" and extended his "heartfelt condolences" to the families of the victims and the people of Iran.
Decades of international sanctions have left Iran with an aging commercial airline fleet, and accidents have increased in recent years. The country has been unable to buy airplane parts for needed maintenance or upgrade its fleet.
Following the 2015 nuclear deal with world powers, Iran signed agreements with both Airbus and Boeing to buy new planes.
Todd Curtis, founder of the website AirSafe.com said Iran was able to keep its planes flying despite sanctions that made it more difficult to buy parts or new aircraft, but that the aviation sector was not able to benefit from working with others in the industry from around the world.
"Many of the things that happen over time in aviation is based on the fact that those professionals who have dedicated their lives to making aviation safer and more efficient, they get a chance to meet each other at conferences, they get a chance to work in different companies over time. In Iran, that’s not so easy to do," Curtis told VOA.
He also said the ATR-72 plane has been operating around the world for 25 years, and that while it has been involved in deadly crashes before, "there has been no ongoing issue, no ongoing controversy with anything about the design of the aircraft or fundamental faults with how the aircraft is handled by airlines."