Christoph Lange, a spokesman for prosecutors in Potsdam near Berlin, said Thursday the number of firms implicated in the inquiry had grown to 50, most of them based in the west of Germany.
The equipment was allegedly exported across the Polish border to Russia, which has a 1995 contract to repair and complete the damaged, German-built Iranian power reactor at Bushehr. Unlike Moscow, Berlin is strictly opposed to any nuclear exports to Iran.
Lange said several of the business people had already been convicted and had received suspended jail terms or fines.
Investigators discovered in 2004 that Russian engineers had bought in 2001 and 2002 a special crane to raise and lower the fuel rods in the Bushehr light-water reactor, which was designed by German engineering company Siemens before the Iranian revolution.
Nuclear experts say it is feasible to obtain weapons-grade radioactive material from such a reactor.
The Bushehr site, begun in 1974, was bombed and badly damaged during the first Gulf War. Because of the German design, standard Russian nuclear equipment would not fit existing reactor parts.
