Iran's judiciary on Tuesday confirmed the detention of three Australian citizens.
"Two of them had taken pictures in military areas and the third (was detained) for spying for a third country," Fars news agency quoted judiciary spokesman Gholamhossein Esmaili as saying.
"The court will decide whether this person (detained for spying) is guilty or not."
Esmaili did not identify the detained people and gave no details about when they had been arrested.
Australia's foreign ministry had said it was providing consular assistance to the families of three Australians detained in Iran after Britain's Times newspaper reported that two British-Australian women and the Australian boyfriend of one of them had been detained in Iran.
Perth-based travel-blogging couple Jolie King and Mark Firkin, who has been documenting their journey from home to Britain on social media, were first revealed as two of those arrested.
Later, the third Australian was identified by her family as Melbourne University lecturer Kylie Moore-Gilbert who specializes in Middle Eastern politics with a focus on Gulf states.
Britain said on Wednesday that it had raised concerns with the Iranian ambassador over the number of dual-nationality citizens detained in Iran and the conditions in which they were being held.