At least 40 people have died after a passenger train in Iran rammed into the back of an intercity express which had broken down, the provincial governor said this afternoon.
More than 100 people were admitted to hospital after the crash in the northern province of Semnan on the main line between the capital Tehran and second city Mashhad, Mohammad Reza Khabbaz told state television.
President Hassan Rouhani ordered an acceleration of rescue efforts as well as an investigation into the cause of the deadly crash in the northern province of Semnan.
Video footage showed four derailed carriages, two of them on fire.
A spokesman for Iran's Red Crescent, Mostafa Mortazavi, told the semi-official Fars news agency that firefighters were trying to control the blaze.
Fars quoted Semnan provincial governor Mohammad Reza Khabbaz as saying the death toll was expected to increase.
The governor of Tabriz told the semi-official Tasnim news agency that the moving train had 400 passengers on board.
It was not clear how many passengers had been on the second train.
Fars had earlier said 100 had been rescued.
"Out of the 400 passengers ... 48 are missing. They might be hospitalised or left the area... but there is a high possibility that they were killed," Rahim Shohratifar told Tasnim.
The semi-official Mehr news agency said four of the dead were railway employees aboard the trains.
Mr Khabbaz told Iranian television it appeared that a train entering the Haft-Khan station on the outskirts of Shahroud ploughed into another that had broken down there.
"The initial investigation suggests that a mechanical failure, possibly caused by cold weather, forced the express train, operating between the cities of Tabriz and Mashhad to stop (at Haft-Khan)," Mr Khabbaz said.
A local official told state TV that the remote location of the crash had slowed rescue efforts.
"So far only one helicopter has reached the scene because of access difficulties," said local Red Crescent chief Hasan Shokrollahi.
Iran's rail network aged badly under economic sanctions imposed over its disputed nuclear programme, making it difficult to modernise rolling stock, and safety standards suffered.
The sanctions were lifted in January after Iran reached a deal with world powers to limit its nuclear activity.
