Some experts fear that Iran might use these reactors in the future to build a nuclear bomb. They say the Bushehr reactor could produce a quarter ton of plutonium per year, which would be enough for at least 30 atomic bombs.

The prosecution office in Potsdam near Berlin has been looking into illegal exports to Iran since Sept. 2004.

Christoph Lange, who is a spokesperson for state prosecutors, said on Thursday that the case was getting bigger every week. The number of German firms involved in the matter has now grown to more than 50.

"They export the technology," Lange said. "That's illegal."

The Russian connection

Lange estimates that the value of illegal German exports might easily exceed 150 million euros ($200 million) in value.

The exports are believed to have been organized by a bogus Russian company situated in Berlin. This company allegedly first transported the equipment across the Polish border to Russia, which has a 1995 contract to repair and complete the German-built Iranian power reactor at Bushehr. Moscow -- unlike Berlin -- doesn't oppose any nuclear exports to Iran.

Because of the German design, standard Russian nuclear equipment would not fit existing reactor parts in Bushehr. The site, built in 1974 by German company Siemens, was bombed and badly damaged during the first Gulf War.

Companies knew the final destination of parts

Lange said prosecutors believed only about 12 firms knowingly broke export restrictions. The rest were innocent, as they had only been invited to tender for the work or had believed the parts were going to Russia. But, Lange adds, "a few of them did know" the true destination of the parts.

According to Lange, several business people involved have already been convicted and have received suspended jail terms or fines. The state attorney now expects even more cases to go to court.