File Photo: French Foreign Minister Catherine Colonna speaks at a press conference at the French Mission on September 19, 2022, in New York. AP
"We are worried about two other compatriots and the last verifications show they are also detained," she told the daily newspaper, Le Parisien.
Last month, Colonna said five were being held in Iran.
"It is more important than ever to remind Iran of its international obligations. If its aim is blackmail, then it cannot work," she said.
"We demand their immediate release and access to consular protection.
"My Iranian counterpart, with whom I had a long difficult conversation, has committed to respecting this right of access. I expect it to be realised."
The identity of the two new detainees was not immediately clear.
The others held include French-Iranian researcher Fariba Adelkhah, arrested in June 2019 and later sentenced to five years in prison for undermining national security, allegations her family has strongly denied.
Another, Benjamin Briere, was arrested in May 2020 and later sentenced to eight years and eight months in prison for espionage, charges he rejects.
French teachers' union official Cecile Kohler and her partner Jacques Paris were also detained in May this year, accused of seeking to stir labour unrest during teachers' strikes.
There is also a "Frenchman who was passing through" Tehran, France has said.
The French government last month advised its citizens visiting Iran to "leave the country as soon as possible".
Iran has been rocked by protests since the death in police custody of young Kurdish woman Mahsa Amini in September, following her arrest for an alleged breach of Iran's hijab dress rules for women.