Iran has acknowledged for the first time that it holds three Australian nationals on suspicion of spying, marking the latest cases of those with Western ties being detained in the country amid tensions between Tehran and the U.S.

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, judiciary spokesman Gholamhossein Esmaili said, without naming them.

He said two Australians, likely the blogging couple Mark Firkin and Jolie King, had been detained over using a drone to take pictures and video of military areas and other unauthorized zones.

He said the other Australian faced charges of spying for another country, without elaborating. That's likely an as-of-yet-unnamed Melbourne academic.

Australia said last week it was pressing Iran to free those held.