TEHRAN – Four carriages derailed and two caught fire when a train that had broken down was hit by another train.
The accident happened in freezing temperatures early on Friday, 250km (150 miles) east of the capital Tehran.
The rescue effort is being hampered by the remote location, officials say. President Hassan Rouhani has ordered an inquiry into the cause of the crash.
The crash occurred in Iran’s northern province of Semnan, on the main line between Tehran and Mashhad in the north-east.
State Governor Mohammad Reza Khabbaz said a mechanical failure caused by the extreme cold had forced the intercity express train to stop between stations.
The head of the province’s Red Crescent Hassan Shokrollahi said: “Because of the difficulty of access, only our helicopter has managed to reach the scene.”
More than 70 people have been taken to hospitals and the death toll is expected to rise, officials say.