The three Americans were captured July 31 after they entered Iranian territory while hiking in northern Iraq. They said they accidentally crossed the border.
They have been charged with illegal entry into the country but that could escalate into espionage, one official suggested last month.
Iranian Foreign Minister Manouchehr Mottaki, at a news conference Monday, said: "Interrogation of the three Americans who have illegally entered Iran with suspicious aims is ongoing. They will be put on trial by the judiciary and rulings will be made."
No trial date was announced.
U.S. Secretary of State Hillary Clinton has called for the release of the hikers.