Iranian investigators have set up several working groups to probe yesterday's fatal Iran Air Boeing 727-200 accident at Urmia.
The aircraft is a 37-year old airframe, registered EP-IRP, fitted with Pratt & Whitney JT8D engines.
The Iranian Civil Aviation Organisation states that the aircraft had been operating as flight IR277 from Tehran when it came down near its destination.
While the aircraft broke into several sections on impact, there is no evidence of fire at the crash site.
The Iranian transport ministry says that an inquiry is underway into the "unsuccessful landing" by the 727. It states that working groups comprising specialists in aircraft structure, pilot operations and engine-parameter recordings will participate.
Source: Iranian Civil Aviation Organisation
Unconfirmed reports from Iranian state media say that 77 of the occupants were killed, from around 104 on board.
There are also confused reports over whether the aircraft conducted a go-around and whether it was attempting to return to Tehran when the accident occurred. The crash site is several kilometres from Urmia, reports say.
Urmia Airport had been experiencing heavy snow and poor visibility at the time. The Iranian Civil Aviation Organisation acknowledges "bad weather conditions" on site.
Iran Air has been subject to US sanctions on commercial aircraft for decades although there is no immediate evidence that the restrictions played a direct role in the crash.