The report did not elaborate on the source of the information, but the agency is regarded as close to Iran's hard-liners.
Iranian officials have said Rezaian is facing "security" charges and that he will stand trial in the Revolutionary Court, which mainly hears cases involving security offenses. Rezaian, along with his wife, Yeganeh Salehi, and two photojournalists were detained on July 22 in Tehran.
All were later released except Rezaian, who is a dual US-Iranian citizen. Iran does not recognize dual nationality.
The Fars report alleged that Rezaian had obtained economic and industrial information from Iran and sold it to unnamed Americans. It also linked him to Omid Memarian, an Iranian opposition journalist based in the US.
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"Selling Iran's economic and industrial information at a time of sanctions is exactly like selling food to the enemy at a time of war," Fars alleged.
Iran is under crippling sanctions over its nuclear program, which Western nations suspect is aimed at developing an atomic weapons capability. Iran insists the program is for purely peaceful purposes.