Cecilia Sala, 29, who works for the newspaper Il Foglio and the podcast company Chora Media, was detained in Tehran on December 19 but her arrest was only made public on Friday.
The Italian foreign ministry said it was in contact with Iran to clarify Sala's legal situation and the conditions of her detention.
"Italy is working tirelessly to free her, pursuing every option," Defence Minister Guido Crosetto - a key figure in Prime Minister Giorgia Meloni's government - wrote on the social media platform X, calling the arrest "unacceptable".
Fin dal primo giorno, da quando è arrivata la notizia dell'inaccettabile arresto di Cecilia Sala da parte delle autorità Iraniane, tutto il Governo, in primis il Presidente Giorgia Meloni ed il Ministro Tajani, si è mosso per farla liberare.— Guido Crosetto (@GuidoCrosetto) Ogni persona che poteva e può essere…December 27, 2024
Chora Media said Sala had left Rome for Iran on December 12 with a valid journalist visa and had conducted several interviews and produced three episodes of her Stories podcast. She had been due to fly back to Rome on December 20.
It added that Sala was being held in solitary confinement in Tehran's Evin prison and no reason had been given for her arrest.
There was no immediate confirmation of the arrest by Iranian officials.
It was not clear whether it might be linked to tensions between Rome and Tehran after Iran last week summoned a senior Italian diplomat and the Swiss ambassador, who represents US interests in the country, over the arrest of two Iranian nationals. One of the men was arrested in Italy at Washington's request.
Italy's ambassador to Iran visited Sala in prison on Friday and the journalist has also been in phone contact with her family, the Italian foreign ministry said.
Italian sources with knowledge of the matter said she was "very tired" but "physically fine".
Chora said news of Sala's arrest was not immediately made public as her family and Italian authorities had hoped that keeping it quiet could help secure her swift release.
Elly Schlein, leader of the centre-left opposition Democratic Party, urged the government to act swiftly.
"We immediately call on the government to take every useful initiative to shed light on this matter, to clarify the reasons for this detention and, above all, to bring Cecilia Sala back to Italy as soon as possible," she said.
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