France said on Tuesday there was no doubt Iran's intelligence ministry was behind a June plot to attack an exiled opposition group's rally outside Paris and it seized assets belonging to Tehran's intelligence services and two Iranian nationals.
The hardening of relations between Paris and Tehran could have far-reaching consequences for Iran as President Hassan Rouhani's government looks to European capitals to salvage a 2015 nuclear deal after the United States pulled out and re-imposed tough sanctions on Iran.
A French diplomatic source said they have reached a conclusion after a long investigation that the Iranian intelligence ministry is "without any doubt" responsible for the attack.
The source, speaking after the government announced asset freezes, added that the deputy minister and director general of intelligence, Saeid Hashemi Moghadam, had ordered the attack and Assadollah Asadi, a Vienna-based diplomat held by German authorities, had put it into action.
Iranian Foreign Ministry has denied the accusation.
"We deny once again the allegations against Iran and demand the immediate release of the Iranian diplomat," the Foreign Ministry spokesman Bahram Qasemi was quoted as saying by state news agency IRNA.
The incident was a plot "designed by those who want to damage Iran's long-established relations with France and Europe," he said.
The attack in June targeted a meeting of the Paris-based National Council of Resistance of Iran (NCRI) outside the French capital.
US President Donald Trump's lawyer Rudy Giuliani and several former European and Arab ministers attended the rally.
It unraveled after Asadi, an accredited diplomat in Austria, was arrested in Germany, two other individuals were detained in Belgium in possession of explosives, and one other individual in France.
On Monday, a court in southern Germany ruled the diplomat could be extradited to Belgium.
"We cannot accept any terrorist threat on our national territory and this plot needed a firm response," the French side said. The asset freezes targeted Asadi and Moghadam. A unit within the Iranian intelligence services was also targeted.
The French government gave no details of the assets involved, describing its measures as "targeted and proportionate."
During the annual UN General Assembly last week in New York, French President Emmanuel Macron and Foreign Minister Jean-Yves Le Drian spoke to their Iranian counterparts about the issue.