TEHRAN, Iran (AP) — A passenger train traveling through eastern Iran struck an excavator and nearly half its cars derailed before dawn on Wednesday, killing at least 22 people and injuring 87, officials said.

The derailment near the desert city of Tabas was the latest disaster to strike the Islamic Republic in recent weeks as Tehran struggles under U.S. sanctions and any return to its nuclear deal with world powers remains in doubt.

The train, operated by the state-run Islamic Republic Railway, carried some 350 people as it traveled from the town of Tabas, some 550 kilometers (340 miles) southeast of Tehran, to the city of Yazd. The route had began as an overnight train out of Iran’s holy city of Mashhad.

Based on images after the crash, it appeared the train’s locomotive passed the excavator and the later cars somehow hit the digger and caused the derailment, though authorities did not immediately explain how the disaster happened in the rural scrubland near a railway bridge.

“Passengers were bouncing in the car like balls in the air,” one unnamed injured passenger told Iranian state television.

The state-run IRNA news agency gave the casualty figures, citing emergency officials.

Rescue teams with ambulances and helicopters arrived in the remote area where communication is poor. Over a dozen people suffered critical injuries, with some transferred to local hospitals, officials said.

Aerial footage of the desert site of the disaster showed train cars on their side, with some rescuers running at the scene as they tried to care for those injured.

State TV later aired images from a hospital where the injured received treatment. One of those injured told the broadcaster they felt the train suddenly brake and then slow before the derailment.

The incident happened some 50 kilometers (30 miles) outside of Tabas.

The report said the crash is under investigation. Initial reports suggested the train collided with an excavator near the track, though it wasn’t immediately clear why an excavator would have been close to the train track in the dark. One official suggested it could have been part of a repair project.

Iran’s President Ebrahim Raisi offered condolences over the crash and announced an investigation would be undertaken into its causes. On Wednesday night, authorities ordered the arrest of six people allegedly involved in causing the crash, though they released no other information about why they were suspected.

Iran’s worst train disaster came in 2004, when a runaway train loaded with gasoline, fertilizer, sulfur and cotton crashed near the historic city of Neyshabur, killing some 320 people, injuring 460 others and damaging five villages. In 2016, a train collision in northern Iran killed at least 43 people and injured about 100.

Iran has some 14,000 kilometers (8,700 miles) of railway lines throughout the country that’s about two and a half times the size of Texas. Its rail system sends both people and goods across the country, particularly in rural areas.

Iran also has some 17,000 annual deaths on its highways, one of the world’s worst traffic safety records. The high toll is blamed on wide disregard for traffic laws, unsafe vehicles and inadequate emergency services.

Iran, already straining under U.S. sanctions over its collapsed nuclear deal, has been mourning the deaths of at least 41 people killed in a building collapse in May in the city of Abadan in the country’s southwest.

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