Iran's official news agency says that an explosion at a steel mill in the central Iranian city of Isfahan has killed three workers and injured four.

IRNA says the explosion happened on Thursday morning when workers were melting scrap metal. The casualties were taken to local hospitals. Isfahan is about 400 kilometers (250 miles) south of the capital, Tehran.

IRNA did not elaborate on the reason for the explosion.

The well-known Isfahan steel mill has nearly 14,000 workers. It is the oldest operating steel mill in Iran and it started working in 1960s, with the help by the Soviet Union.

Apart from the plant in Isfahan, Iran has two other major steel mills.