Bauer, Fattal and Shourd were arrested in July 2009 after illegally crossing the border into Iran from the mountains of northern Iraq's Kurdistan region.
Shourd was not present at the first session of the trial; however, her lawyer submitted a statement on her behalf.
The three have pleaded not guilty.
The Tehran Prosecutor's office says it has 'compelling evidence' that three were cooperating with US intelligence agencies.
No date has been confirmed for the next court session.
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