At least 21 people have been killed and dozens more hurt after a train derailed in eastern Iran, state media report.
The train, which was carrying 348 passengers, came off the line between the cities of Mashhad and Yazd about 50km (31 miles) from Tabas.
The deputy head of Iran's railways said the accident happened when the train hit an excavator near the track.
Emergency services warned the death toll could rise because many of the injured were in a critical condition.
Five of the train's 11 carriages were knocked off the line, Mehdi Valipour of the Iranian Red Crescent told state TV.
Pictures posted online by local media showed several carriages on their side, as well as a yellow excavator on its side beside the track.
National rescue service spokesman Mojtaba Khaled told reporters that three helicopters and 24 ambulances were dispatched to the scene after the accident, which happened at around 05:30 local time (01:00 GMT).
State TV broadcast footage from a local hospital where the injured were receiving treatment. One of them told a reporter that they felt the train brake suddenly and then slow before the derailment.
An investigation has been launched by the Tabas prosecutor to establish how the train came to strike the excavator.
One official suggested that the excavator might have been part of a repair project, the Associated Press news agency reported.
The accident comes after a 10-storey building collapsed last month in the south-eastern city of Abadan, killing 43 people and sparking protests in which people denounced the authorities for negligence and corruption.
Iran saw its deadliest train disaster in 2004, when a train loaded with petrol, fertilizer and cotton crashed near the north-eastern city of Neyshabur, killing almost 320 people.
And in 2016, 49 people were killed when a train that had broken down was hit by another train in the northern province of Semnan.