German prosecutors said four men were arrested Wednesday, suspected of delivering equipment to Iran for use in a nuclear reactor the West fears could be used as part as a covert weapons programme.

Three men with joint Iranian-German nationality, identified only as Kianzad Ka., Gholamali Ka. and Hamid Kh., and German national Rudolf M. were picked up early Wednesday by a force comprising 90 officers.

"The accused are believed to have contributed in 2010 and 2011 to the delivery of special valves for the construction of a heavy water reactor in Iran and thereby contravened the Iran embargo," prosecutors said.

The four are accused of breaking both an arms embargo and export restrictions on goods that can be used for both civil and military purposes.

Western powers suspect that Iran wants to develop nuclear weapons, an accusation Tehran denies.

Iran is currently building a heavy water plant in Arak, central Iran. Iran says the plutonium the plant will produce is for medical research.

But the West fears the plant could be used to produce plutonium for a potential bomb.

In order to circumvent the export ban, the four men arrested are believed to have said the parts were for companies based in Turkey and Azerbaijan.

Authorities raided their homes and businesses as well as those of a fifth suspect, who was not named.