Australia has said it is providing consular assistance for the three detainees. (Representational)

Iran has charged three detained Australians with spying, Tasnim news agency reported Tuesday, citing judiciary spokesman Gholamhossein Esmaili.

Two of the Australians were alleged to have used a drone to take pictures of military sites, while a third was accused of spying for another country, Esmaili said in the report, without naming them.

It was the first official confirmation that Australians have been detained in Iran after the families of three of them said last week they had been arrested in the Islamic republic.

They identified them as a travel-blogging couple Jolie King and Mark Firkin and Melbourne University lecturer Kylie Moore-Gilbert.

"The news is correct," Esmaili said according to Tasnim, adding the matter involved two separate cases.

"One case is of two people taking photos of military sites and our forbidden areas," he was quoted as saying.

They had been identified at the time and images were found on a drone they were using, he added.

The other case involved an individual accused of "spying for another country", said Esmaili.

"Criminal charges have been issued for both cases and they are waiting for their trial," he was quoted as saying.

Australia has said it is providing consular assistance for the three detainees.

Australian Foreign Minister Marise Payne said there was "no reason" to believe the arrests were politically motivated.