Four men have been arrested in Germany on suspicion of illegally supplying Iran with parts needed to build a nuclear reactor.
The suspects were held following searches of homes and business in Hamburg, Oldenburg and Weimar.
They are accused of using front companies in Turkey and Azerbaijan to supply the parts in deals worth millions of euros.
Germany has an embargo on nuclear-related trade with Iran.
Many Western countries have concerns about Iran's nuclear programme, but Iran insists it is for peaceful purposes.
Prosecutors say the group, which includes one German national, and three Iranian-German dual nationals, were supplying speciality valves to be used in heavy water reactors.
They are accused of breaking the arms embargo, as well as export restrictions on goods that could be used for military purposes.
Prosecutors say the men, known as Rudolf M, Kianzad Ka, Gholamali Ka, and Hamid Kh, knew what the parts would be used for.
Germany privacy laws prevent their full names being released.
A fifth suspect has not been named.
Some 90 customs officials and prosecutors were involved in the searches that led to their arrest.
The men will appear in court on Wednesday.