TEHRAN (Iran) — An Iranian passenger train was partially derail in eastern Iran on Wednesday morning, killing at least 17 and injuring 50 others, according to authorities.

Although the report indicated that the number of casualties could increase, initial details regarding the train accident that reportedly killed 350 people remain unclear.

Iranian state television reported that four of seven cars on the train were derail in the early morning darkness close to Tabas. Tabas lies approximately 550 km (340 miles) southwest of Tehran, the capital.

In remote areas where communication is difficult, rescue teams arrived with helicopters and ambulances. Officials said that more than a dozen people sustained critical injuries and were being transferred to local hospitals.

Iranian media reported that Ali Akbar Rahimi, the governor of Tabas said the crash claimed at least 17 lives and that there may be more deaths as rescuers search for the train cars.

Aerial footage showed that train cars were on the side of the disaster site, and some rescuers ran at the scene to help those who were injured.

Later, images were broadcast by state TV from the hospital where the injured were treated. One of the injured said that the train braked suddenly and then slowed before it derailment.

“Passengers were bouncing around in the car like balls in air,” stated the injured passenger, who state TV didn’t identify.

The train that connects Tabas to Yazd was derailment at 50 km (30 miles) from Tabas.

According to the report, an investigation is underway into the cause of the crash. Initial reports indicated that the train collided near the track with an excavator, but it was not immediately clear why an excavator would be so close to the train track at night. Officials suggest that it was part of a project to repair the track.

Iran’s worst train accident occurred in 2004 when a train carrying gasoline, fertilizer and sulfur collided near Neyshabur. It killed 320 people and injured 460 more. Five villages were also damaged. In 2016, another train accident resulted in the deaths of dozens of people and injured scores more.

Iran boasts 14,000 km (8,700 miles), of railway lines in a country that is almost twice the size of Texas. The country’s railway system transports people and goods, especially in rural areas.

Iran has one of the worst traffic safety records in the world, with 17,000 deaths per year on its highways. This high death toll can be attributed to widespread disregard for traffic laws, unsafe vehicles, and insufficient emergency services.

Iran is already under severe sanctions from the United States for its collapsed nuclear agreement.