* Attempted bombing targeted exiled Iranian group
* Hardening of relations could have wide implications for Iran
* Asset freeze targets Iranian intelligence unit (Adds U.S. State Department comment)
By John Irish and Richard Lough
PARIS, Oct 2 (Reuters) - 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 reimposed tough sanctions on Iran.
"Behind all this was a long, meticulous and detailed investigation by our (intelligence) services that enabled us to reach the conclusion, without any doubt, that responsibility fell on the Iranian intelligence ministry," a French diplomatic source said.
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.
The ministry is under control of Supreme Leader Ayatollah Ali Khamenei.
"We deny once again the allegations against Iran and demand the immediate release of the Iranian diplomat," Iranian 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 plot targeted a meeting of the Paris-based National Council of Resistance of Iran (NCRI) outside the French capital. U.S. President Donald Trump's lawyer Rudy Giuliani and several former European and Arab ministers attended the rally.
It unravelled 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 diplomatic source said.
TARGETED ASSET FREEZES
In a news briefing in Washington, U.S. State Department spokeswoman Heather Nauert noted the French action and said it was evidence that "there’s probably no one who has felt terrorism stemming from Iran perhaps more than - well, the Syrians - that has felt it more than some Europeans."