Armando Spataro, Italy's anti-terrorism chief, said the police operation was of "considerable importance because it concerns the entire international community".
Called 'Operation Sniper', the investigations began in June 2009 and involved extensive wiretapping and searches of more than 20 sites in nearly a dozen Italian provinces, he said.
A police statement said those arrested were wanted for "criminal association for the purpose of exporting arms and weapons systems to Iran in violation of the international embargo that is in effect".
Sabina Castelfranco, Al Jazeera's correspondent in Milan, said one of the arrested Iranians was a journalist who had been working for Iranian state television in the country for around 17 years.
Colonel Vincenzo Andreone of the financial police, who led the operation, said some of the Italians arrested were "entrepreneurs, the heads of various import-export or communications businesses".
"They had set up a triangular system to cover their tracks. The trafficking was taking place at least since 2007."
Andreone said they bought weapons in Europe, mainly in Europe, then transported the arms through third countries such as Britain, Switzerland and Romania before shipping them to Iran.
The scheme fell apart during a check by Romanian customs officials, who confiscated 200 gunsights. Another 100 were seized in London, he said.
He said police in Bern, Switzerland, where one of the Italian suspects resided, had collaborated with the investigation.
British authorities arrested a Briton implicated in the trafficking a few months ago, Spataro added.
Silvio Berlusconi, the Italian prime minister, has previously said that trade sanctions against Iran, which is subject to an international arms embargo, should be tightened.
Mehrdad Khonsari from the Centre for Arab and Iranian Studies told Al Jazeera that relations between Iran and Italy, which is one of the EU's biggest trading partners with Tehran, have soured since Berlusconi took office.
"The Iranian authorities think that Mr Berlusconi has been a little over-aggressive against them compared to the previous [Romano] Prodi government.
"But the fact is that any revelation of this nature does not enhance bilateral relations and the Iranians will deny it and will try to say that they're not involved, or that the persons involved are not intelligence officers."