German prosecutors said Monday they had charged four men with breaching sanctions against Iran by delivering equipment for an atomic reactor that the West suspects is part of a covert nuclear 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 arrested last August in police raids involving 90 officers.

They were charged last Friday in a Hamburg court, prosecutors said.

The four are accused of having delivered special valves for a heavy water reactor in 2010 and 2011, in breach of an arms embargo and export restrictions against Iran on goods that have dual civil and military purposes.

Western powers suspect Iran wants to develop nuclear weapons, a charge Tehran denies.

The Islamic republic is building a heavy water plant in Arak, central Iran, and says the plutonium it will produce is for medical research.

The prosecutors in their statement said "there is a concern that this reactor will be used to produce nuclear-weapons-grade plutonium."

The German-Iranians, aged 25 to 80, and the 78-year-old German are accused of having colluded to send the parts via several Asian countries in deals worth several million euros (dollars).

They allegedly sent five shipments with a total of 92 German-made special valves and also brokered another four deliveries with a total of 856 valves for use in nuclear plants from India.

The order came from a 48-year-old Iranian national, who is also wanted by German authorities, and who was using companies set up in several other countries to circumvent the embargo against Iran, said prosecutors.

The suspects Gholamali Ka. and his son Kianzad Ka. remain in custody. Alleged middleman Hamid Kh. and Rudolf M., who heads a company in the state of Thuringia that made some of the valves, have been released on bail.