An investigation has been launched into the cause of the leak of nitrogen gas from a soda ash production plant in the city of Firuzabad, the official IRNA news agency said.

"The injured mostly suffered from respiratory problems caused by nitrogen gas, which is not dangerous," the crisis management director for Fars province, Khalil Abdollahi, was quoted as saying.

No one was killed and most of those hospitalised have since been discharged, a provincial medical official said.

Opened in 2020, the Firuzabad Sodium Carbonate Factory has an annual production capacity of 320,000 tonnes, IRNA said.

Also known as soda ash, sodium carbonate is mostly used in the manufacture of detergents, soaps, paper, glass and petrochemical products.