Sakineh Mohammadi Ashtiani, a 43-year-old mother-of-two, has been sentenced to death in an Iranian court after being convicted of engaging in an extramarital affair. Bruni-Sarkozy recently signed an open letter calling for Ashtiani's immediate release.
Deneuve asserted that Bruni-Sarkozy's public remarks allowed Iranian hardliners to discredit the cause because of the French first lady's own alleged past infidelities, according to The Daily Telegraph.
"When you are a famous person you need to be more cautious when you lend your support to causes – with her past she should have been more careful. It can be a double-edged sword," the actress explained.
The César-winning star continued: "The other side just took the ball on the bounce. Their hint at her private life was as if to say, 'Mind your own business'."
Bruni-Sarkozy previously admitted that she easily grows "bored with monogamy".