Sixty-six people are feared to have been killed in a passenger plane crash in the Zagros mountains in Iran.
The Aseman Airlines plane, en route from Tehran to the south-western city of Yasuj, came down near the city of Semirom in Isfahan province.
The Red Crescent deployed search and rescue teams to the site. The airline has retracted a statement saying definitively that all aboard were dead.
Flight EP3704 left Tehran at 04:30 GMT, and crashed about an hour later.
The aircraft, a twin-engine turboprop, came down on Dena Mountain, 22km (14 miles) from Yasuj, news channel Irinn reported.
Sixty passengers, two security guards, two flight attendants and the pilot and co-pilot were on board.
The airline initially said everyone had been killed, but said later: "Given the special circumstances of the region, we still have no access to the spot of the crash and therefore we cannot accurately and definitely confirm the death of all passengers of this plane."
Bad weather, including fog and heavy snow, has hampered rescue efforts. Emergency teams have had to travel to the crash site by land rather than using a helicopter.
Passengers' relatives have gathered at a mosque near Tehran's Mehrabad airport, according to Reuters news agency.
"I can't bring myself to believe it," said one woman whose husband was on board.
One man told Tabnak news website that he had missed the flight.
Showing an unused ticket as proof, he said: "God has been really kind to me but I am so sad from the bottom of my heart for all those dear ones who lost their lives."
Iran's President Hassan Rouhani expressed sympathy for all involved, saying, in a statement, that the incident brought "great grief and sorrow".
Iran has suffered several aviation accidents in recent years and has an ageing aircraft fleet.
The country has struggled to obtain spare parts to maintain its planes in the face of international sanctions imposed to curb its nuclear programme.
Those sanctions have been mostly lifted under a 2015 deal between Iran and the US alongside several other powers.
Aseman, Iran's third largest airline, signed a contract with Boeing last year to buy 30 of its latest medium-range 737s.
The crashed plane, a French-Italian-made ATR 72-500, was 25 years old, Iran's civil aviation organisation said.
Iran's Supreme Leader, Ayatollah Ali Khamenei, has also expressed "deep sympathy" for relatives of those on board, saying the accident "saddened the hearts".
Recent major air crashes in Iran
August - Sepahan airways Antonov carrying 40 crashes shortly after take-off from Tehran, killing 39 - engine failure blamed
Caspian Airlines Tupolev bound for Armenia from Tehran catches fire shortly after take-off killing all 168 on board