France rejected an Iranian protest over allegations of a state-directed plot to bomb an opposition rally near Paris last week, saying it would proceed with the extradition of a suspect to Belgium, where the attack was masterminded.
Germany also plans to extradite an Iranian diplomat who was dramatically arrested on the autobahn having been implicated in the pan-nation conspiracy.
The arrest of the Vienna-based counselor in Iran's diplomatic service enraged Tehran, where the foreign ministry called in French, Belgian and German representatives to make a formal complaint about the arrests.
Afterwards the French foreign ministry said it did not accept the Iranian protestations that the opposition group, known as the National Council of Resistance in Iran (NCRI), had plotted to bomb its own event in Villepinte, near the capital.
"On the planned attack at Villepinte, an investigation is in progress. It will have to determine the real sponsors of this projected attack," a French diplomatic source said.
Belgium is investigating two citizens of Iranian origin who were arrested on Saturday, the day of the NCRI meeting, which was attended by US President Donald Trump’s lawyer Rudy Giuliani and the former Canadian prime minister Stephen Harper.
The vehicle the couple was using was found to contain 500 grams of the homemade explosive TATP and a detonation device.
Iran has said it had nothing to do with the plot, which it called a “false flag” operation staged by figures within the opposition group itself.
In addition to the two people arrested in Belgium, a man of Iranian origin was held in France.
“It’s extremely sensitive and the Belgians are taking the lead,” a European intelligence official was quoted as saying.
During a visit by Iranian President Hassan Rouhani to Vienna on Wednesday, Austrian Chancellor Sebastian Kurz demanded clarity on the case.
Iran's foreign ministry also accused France of supporting the NCRI, which seeks the overthrow of the Islamic Republic and is classified by Tehran as a terrorist organisation.
But the French retorted that the Iranians were wrong. "France supports neither the ideology, objectives nor activities of the [NCRI]. However, having been removed from the European list of terrorist organisations, this organisation can carry out, like any other association, activities, as long as they do not undermine public order," a French diplomat said.
French judicial sources said on Wednesday they had received a request from Belgium to extradite a man of Iranian origin who was arrested in Paris on suspicion of links to the plot.
Meanwhile, Israel's prime minister hinted that his country had played a role in detecting and disrupting the plot. Benjamin Netanyahu said the involvement of the Iranian state should prompt a European rethink on the strategic decision to sustain the 2015 nuclear agreement. Europe has rejected Washington's decision to repudiate the deal as a catalyst for Iranian meddling in the region.
"It was no coincidence that this attack was thwarted," Mr Netanyahu said. "I call on the leaders of Europe: stop financing the terrorist regime that is financing terrorism against you on your soil. Enough with the policy of appeasement and weakness regarding Iran."
The NCRI is a lavishly funded movement based on the exiled Mujahideen-e-Khalq, which was driven out of Iran in fighting after the revolution. It was listed as a terrorist organisation by the United States and the European Union until 2012.
Tehran has long called for a crackdown on the NCRI by Paris, Riyadh and Washington. The group is regularly criticised in state media, which on Thursday said the attack was plotted by the group itself to sabotage Mr Rouhani's visit to Austria and Switzerland.