Foreign Minister Bernard Kouchner insisted that Paris would not bow to what he said was pressure from President Mahmoud Ahmadinejad to swap 24-year-old Clotilde Reiss's freedom for that of Iranian convict Ali Vakili Rad.
"What does he want? He wants to make us swap Clotilde Reiss for Vakili Rad, that's to say the assassin of Shapour Bakhtiar. It's out of the question," Kouchner said, at a breakfast for foreign journalists in Paris.
"Even if we wanted to, we couldn't," Kouchner said, citing France's laws about the independence of the judiciary, which sentenced Vakili Rad to life imprisonment in 1994, setting a minimum term of 18 years.
On Friday, Ahmadinejad said that he would like to allow Reiss to return to France, but that the decision would "depend on the French authorities". He did not specify what he wanted Paris to offer in exchange.
In September, France's President Nicolas Sarkozy angrily rejected the idea of swapping an "innocent young woman" for Bahktiar's killer, after Ahmadinejad had raised the issue of several Iranians in French jails.
In 1994, a French court found Vakili Rad guilty of murder after he admitted to carrying out the 1991 murder in the Paris suburbs of Bakhtiar, an Iranian exile who had served as prime minister under the former Shah of Iran.
Vakili Rad was arrested in Switzerland and extradited to France, where he told a court he had been sent by Iran's Islamic government to kill Bakhtiar, a target because he had worked under the ousted Shah's hated regime.
Reiss was arrested in the wake of the protests that followed Iran's disputed presidential election in June, shortly before she was due to fly home after a six-month study and teaching visit to the Iranian city of Isfahan.
She was accused of supporting the opposition protests and was one of scores of alleged dissidents paraded before cameras at a televised show trial, before being remanded in custody in Tehran's notorious Evin jail.
In August, Reiss was granted bail on condition that she await the final verdict in the case at the French embassy in Tehran, where she has remained.
"She's been summoned on Wednesday for a new court hearing, her last. I'm in favour of her going," Kouchner said at the Paris breakfast.
Iran has been in turmoil since June's election, which opposition supporters claim Ahmadinejad stole from rival Mir Hossein Mousavi in a rigged ballot.
Hundreds of alleged demonstrators have been rounded up during months of street protests, and Tehran initially alleged that Reiss had been acting as a spy and agent provocateur when she attended an Isfahan rally.
France along with Reiss' anxious family has firmly rejected that accusation, but the Tehran regime now seems keen to use the young woman as a diplomatic bargaining chip, amid tensions with the West over its nuclear programme.
Along with the United States, France has been one of the loudest voices pushing for new international economic sanctions against Iran, which it alleges is trying to enrich enough uranium to build a nuclear bomb.
Tehran insists its uranium enrichment programme is intended to provide fuel for an eventual civilian nuclear power plant, and has insisted that it has every right to pursue this programme.
