Two trains collided and caught fire Friday in a remote region of northern Iran, killing 44 people and injuring dozens more, in one of the country's worst rail disasters.
Provincial governor Mohammad Reza Khabbaz told state television that the crash took place in Semnan province on the main line between Tehran and Iran's second city Mashhad.
An express train operating from Tabriz in the northwest to Mashhad had stopped, Khabbaz said, initially suggesting the cause could have been mechanical failure or extreme cold, although it was later put down to human error.
Two coaches on the express burst into flames when a passenger train behind smashed into the back of it at 7:50 am (0420 GMT).
The front four coaches of the second train -- running from Semnan to Mashhad -- derailed and overturned.
"One minute I was sleeping and the next I was being carried out of a coach on fire," one hospitalised passenger told state television.
Television broadcast images of a huge column of black smoke and flames shooting into the sky from coaches with their windows shattered, as firefighters battled the blaze and rescue workers searched for victims.
With the toll climbing throughout the day, Hossein Kulivand, head of Iran's emergency services, said late Friday that 44 people were killed and 82 hospitalised, of whom 17 were treated for light injuries and released.
Human error was determined to have caused the accident.
"For some unknown reasons due to human fault, the train (from Semnan) was ordered to move and so it hit the other train from behind," said Mohsen Poor-Seyed Aghaie, the head of Iranian railways.
- Injured airlifted -
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The province's Red Crescent director, Hassan Shokrollahi, said the remote location of the crash site, between Semnan and Damghan, the next major town, had complicated rescue efforts.
"Due to the difficulty of access, only our helicopter has managed to reach the scene," he said.
The injured were airlifted to hospitals in Semnan and Damghan.
The Tehran-to-Mashhad line was briefly closed to allow an investigation into the cause of the crash, said Sadegh Sokri, spokesman for Iran's railways.
A collision on the same line between a freight train and a passenger train left two dead and 30 injured in June 2014.
President Hassan Rouhani called for "all technical, administrative and preventive measures to be taken to prevent the recurrence of such an accident".
Iranian trains have been involved in four collisions this year with road vehicles, including a crash with a truck in July that left around 30 injured near the Caspian Sea in the northern province of Mazandaran.
Collisions between trains are rarer.
In the country's deadliest rail disaster, 328 people were killed when a train transporting sulphur, petrol and fertilisers exploded in northern Iran on February 18, 2004.
Iran's roads are notoriously deadly, mainly because drivers show scant regard for rules, with 16,000 lives lost in the Iranian year between March 2015 and March 2016.
In a sign of progress, however, an average of 28,000 deaths a year were registered on Iranian roads a decade ago.