The Federal Prosecutor's Office said on Monday Hans-Josef H., a businessman from the southwestern state of Rhineland-Palatinate, was suspected of arranging the export of "proliferation-related wares" to Iran with a Turkish partner between May 2007 and June 2008.
Delivery of the materials, destined for an organization on an embargo blacklist, was prevented thanks to the arrest, the office said in a statement.
German law and United Nations sanctions prevent individuals or companies from supplying Iran with goods intended for nuclear or military uses.
Germany is one of Iran's largest trading partners in the European Union, but its firms have been under pressure from the United States to cut their ties to the Islamic Republic.
The West fears Iran is trying to build nuclear weapons, but Tehran says its nuclear program is for peaceful civilian energy purposes.
(Writing by Noah Barkin; editing by Andrew Dobbie)
