An Iranian court is holding a closed-door session to begin proceedings against three Americans detained 18 months ago and accused of spying.

Authorities imposed a blanket ban for observers, including Swiss Ambassador Livia Leu Agosti who represents U.S. interests in Iran.

The Americans were detained in July 2009 along the Iraqi border. They claim they were hiking in Iraq's Kurdistan region and — if they crossed into Iran — it was inadvertent.

One of the Americans, Sarah Shourd, was released on bail in September. Two others, her fiance Shane Bauer and Josh Fattal, remain in custody.

It was unclear whether the two men were present Sunday in the Tehran Revolutionary Court, which deals with security-related charges.