PARIS (Reuters) - France and Germany will send two men, including an Iranian diplomat, to Belgium to face accusations they were involved in a plot to bomb an Iranian opposition rally on the outskirts of Paris, judicial sources said on Wednesday.

Belgium is already investigating two Belgians of Iranian origin arrested on Saturday, the day of the National Council of Resistance of Iran (NCRI) meeting. Five hundred grams of the homemade explosive TATP and a detonation device were found in their car.

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.

The exiled Iranian opposition group’s meeting was attended by Donald Trump’s lawyer Rudy Giuliani, who gave a speech calling for the removal of Iran’s rulers.

In addition to the two people arrested in Belgium, an Austria-based Iranian diplomat was held in Germany, and a man of Iranian origin was held in France. Judicial authorities in France and Germany told Reuters Belgium had requested they be extradited.

“It’s extremely sensitive and the Belgians are taking the lead,” said one European intelligence source.

During a visit by Iranian President Hassan Rouhani to Vienna on Wednesday, Austrian Chancellor Sebastian Kurz said in a statement to reporters that Rouhani had assured him that he would work to clarify the case.

French officials have declined to comment on the matter saying the nature of the incident is unclear.

Highlighting the political sensitivities, Iran summoned France’s ambassador to protest against the staging of the opposition meeting. Tehran “strongly protested against the French support of activities of the terrorist organization,” referring to an exiled opposition group.

France’s foreign ministry did not immediately respond to a request for comment.

Since the United States withdrew in May from a deal to lift sanctions on Iran in return for curbs to Tehran’s nuclear program, the deal’s European signatories Britain, France and Germany have said they want to save the accord. Iran has called on the European countries to offer economic benefits to make up for the damage caused by new U.S. sanctions.

Any suggestion that Iranian authorities were behind the plot in France could make it politically difficult for leaders, especially French President Emmanuel Macron, to continue to back the nuclear deal.

The Austrian Foreign Ministry said on Tuesday it was stripping the diplomatic status of the diplomat arrested in Germany. Iran’s foreign ministry has rejected as baseless the allegations against the diplomat.