"Our initial estimate is that restarting these units will take at least six months and up to one year," Mehran Pakbin, deputy head of operations at the Khuzestan Steel Company, was quoted as saying by the Mizan Online website on Thursday.

Mobarakeh Steel Company in the central province of Isfahan said that its "production lines have completely shut down following the high volume of attacks".

Both plants have suffered repeated strikes since last week.

"All modules and steelmaking furnaces of this industrial complex have been damaged," Pakbin was quoted by Mizan as saying.

Mobarakeh Steel said late Wednesday on its website that after the attacks, "continuation of operations is not possible".

Iran's Revolutionary Guards have since launched launched missile and drone strikes on industrial areas across the region and Israel in retaliation for the attacks on the steel plants.

The Guards also threatened further retaliation if such attacks happened again.

Steel is a strategically important material used in industrial and military production, including of missiles, drones and ships.

Iran has been at war with the United States and Israel since February 28, when strikes killed the country's supreme leader and triggered a conflict that has since spread across the region.