Authorities on Monday raised the death toll in a plane crash in northwest Iran to as many as 77 as investigators searched for clues to what caused the aircraft to attempt a disastrous emergency landing.

The pilots of the Boeing-727, operated by Iran's national airline, reported a technical failure to the control tower before trying to make the emergency landing in a snowstorm Sunday night, state-run TV reported.

The IranAir aircraft broke into several pieces, but Mahmoud Mozaffar, head of the rescue department of Iran's Red Crescent Society, said there was no explosion or fire.

Heavy snow hampered rescue efforts, the semiofficial Fars news agency cited the head of the state emergency center, Gholam Reza Masoumi, as saying. That report also mentioned fog in the area.

State TV aired footage showing rescue workers and local farmers searching for survivors Sunday night in parts of the wrecked plane under snowfall and in the darkness.

State TV said the aircraft disappeared from radar and went down in farmland after making a second attempt to land. The nature of the technical failure was not clear.

A provincial official, Javad Mahmoudi, said 77 people died and 27 were injured, some critically.

But Iran's Transport Minister Hamid Behbahani said 105 passengers and crew were on board, 72 died and 33 were lightly hurt. There was no word on the fate of the two children he said were on board.

Shortly after the crash, authorities said the plane was carrying 106 people and 71 died. The conflicting accounts could not be immediately explained.

Some of the passengers were able to walk off the plane, said Abbas Mosayebi, a spokesman for the civil aviation authority.

The aircraft was headed from Tehran to Orumiyeh, capital of West Azerbaijan province, a distance of about 460 miles, or 700 kilometers.

Iran has a history of frequent air accidents blamed on its aging aircraft and poor maintenance. Many of the Boeing aircraft in IranAir's fleet were bought before the country's 1979 Islamic Revolution, which disrupted ties with the U.S. and Europe.