"We have a glimmer of hope. We hope that a rapid solution will be found," he said in an interview with RTL radio.
Chatel, who is also education minister, said he based his optimism on the "diplomatic contacts and contacts at the highest level" had by President Nicolas Sarkozy, who has declared the release of Reiss a top priority.
"There has been a development," Chatel said, "but to optimise the chances of success of the negotiations and discussions which are ongoing" he refused to make further comment.
"Clotilde Reiss is innocent" and has been "the victim of a parody of a trial", he reiterated. "We have demanded and will continue to demand her liberation."
Reiss, a lecturer, and French embassy staffer Nazak Afshar, were among defendants tried on charges related to huge protests across Iran after President Mahmoud Ahmadinejad was declared re-elected in June.
According to the Iranian news agency IRNA the 24-year-old French woman admitted in court that she had filed a report on the protests in the city of Isfahan to the cultural department of the French embassy in Tehran.
