Cecilia Sala, 29, works for the newspaper Il Foglio and for podcast company Chora Media. She was arrested by police in Tehran on December 19, the ministry said in a statement.
Italy's government "has worked with Iranian authorities to clarify Cecilia Sala's legal situation and verify the conditions of her detention", the statement said.
Chora Media said in a separate statement that Sala was being held in solitary confinement in the Evin prison in Tehran and that 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 U.S. interests in the country, over the arrest of two Iranian nationals. One of the men was arrested in Italy at Washington's request.
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.
The Italian ambassador to Iran visited Sala in prison on Friday, the ministry and Chora said. The journalist has also been in phone contact with her family, they said.
Chora said news of her arrest was not immediately made public as her family and Italian authorities had hoped that keeping it quiet could help secure her swift release.
The foreign ministry urged the media to exercise "maximum discretion" over the case, while Chora launched a #FreeCecilia hashtag.
"Her free voice has been silenced, and neither Italy nor Europe can tolerate this arbitrary arrest. Cecilia Sala must be freed immediately," Chora said.
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