The foiled plot has sparked growing anxiety in France, Germany and several other countries, including the United States and Israel, that Iran is planning audacious terrorist attacks and has stepped up its intelligence operations around the world.

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Iranian leaders — under pressure from domestic protesters, Israeli intelligence operatives and the Trump administration, which is reimposing economic sanctions lifted under President Barack Obama — are making contingency plans to strike at the country’s adversaries in the event of open conflict, according to American, European, Middle Eastern and Israeli officials and analysts who spoke on the condition of anonymity to discuss sensitive intelligence.

Iran has assigned different units and organizations to conduct surveillance of opposition figures, as well as Jewish and Israeli organizations, in the United States and Europe, the officials said. The Iranians are preparing what one Israeli official called “target files” of specific people or groups that Iran could attack.

One Middle Eastern intelligence official, speaking on the condition that his name and nationality be withheld, cited a “definite uptick” in the level of activity by Iranian operatives in recent months, adding that the Iranians are “preparing themselves for the possibility of conflict.”

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Iran’s reach extends to the United States. In August, the Justice Department arrested two Iranian men, one a dual national with U.S. and Iranian citizenship and the other an Iranian who is a legal U.S. resident, on suspicion of spying on behalf of Iran. The pair are accused of conducting surveillance on a Jewish organization in Chicago and rallies in New York and Washington that were organized by the Mujahideen-e Khalq, or MEK, a dissident group that seeks regime change in Iran.

But the case of the Iranian diplomat is the most alarming, officials and analysts said, and has strained Iran’s diplomatic relations with Germany and France. Both countries are trying to hold together a landmark 2015 agreement meant to curb Iran’s nuclear weapons program, which the Trump administration has abandoned.

The diplomat, Assadollah ­Assadi, has been a high-ranking official in Iran’s embassy in Vienna since 2014 but is also suspected of being the station chief of the Ministry of Intelligence, or MOIS, according to officials from the United States and ­Europe.

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In late June, European intelligence services tracked Assadi as he met with a married couple of Iranian descent living in Belgium and — according to the couple, who spoke to police after their arrest — gave them about a pound of explosive material and a detonator, the officials said.

French, German and Belgian officials say the couple, Nasimeh Naami and Amir Saadouni, who were both born in Iran, planned to bomb a huge MEK rally in Paris, attended by thousands of people, including Rudolph W. Giuliani, President Trump’s personal lawyer and a vocal defender of the group.

European officials said the couple, who are cooperating with authorities, identified Assadi as their longtime handler. Assadi professes not to know them, according to German officials, who said Iranian authorities have claimed he was set up. The Iranian government has said publicly that the plot was fabricated to falsely implicate the regime in terrorism.

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A spokesman for the Iranian mission to the United Nations denied that Iran had planned to attack the rally in Paris, calling the allegations “categorically false.” And he accused the MEK and Israel of staging the plot “to sabotage Iran-E.U. relations.”

“The MEK had long been listed as a terrorist group by the E.U. and the U.S.; it also has a long history of propaganda and false-flag operations,” said the spokesman, Alireza Miryousefi.

The U.S. State Department removed the MEK from a list of designated terrorist organizations in 2012. The group has publicly denied any involvement in the attempted attack in Paris.

Authorities said that Belgium would take the lead in the case for now, since the couple were arrested and have citizenship there.

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French officials have publicly accused Iran’s Intelligence Ministry of planning the attack and have frozen the assets of two suspected intelligence operatives. “This extremely serious act envisaged on our territory could not go without a response,” France’s interior, foreign and economy ministers said in a joint statement. “In taking this decision, France underlines its determination to fight against terrorism in all its forms, particularly on its own territory.”

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French police also raided the headquarters of one of the largest Shiite Muslim centers in France, which has links to Iran, according to European officials, and arrested three people.

Belgian officials contend that Assadi, who was surrounded at the gas station while traveling with his wife and two sons, is not protected by diplomatic immunity from prosecution because he was arrested outside Austria.

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The case has been closely watched by the Trump administration. Assadi’s arrest “tells you, I think, everything you need to know about how the government of Iran views its responsibilities in connection with diplomatic relations,” White House national security adviser John Bolton told reporters this month. Bolton, a prominent Iran hawk, has been leading Trump administration efforts to place new sanctions on Iran, which he called “the central banker of international terrorism.”

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The MOIS has a long history of conducting surveillance operations in Europe, but an attack at a major public gathering in Paris, attended by Trump’s lawyer, would invite massive retaliation from the French and the Americans, prompting some experts to wonder why Iran would take such a risk.

Iran has in the past targeted Iranian dissidents abroad, and Tehran has previously been linked to numerous plots involving Israeli, Jewish and Arab interests in the West. The level of Iranian activity ebbs and flows, sometimes without a discernible reason, according to former U.S. officials and Iran experts.

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In the first 15 years after Ayatollah Ruhollah Khomeini came to power as supreme ruler in 1979, Iranian agents assassinated at least 60 people in four European countries. The most notorious single attack was the 1992 assassination of a Kurdish Iranian dissident leader and three of his colleagues, all shot inside a Berlin restaurant.

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Some experts now fear a return to those kinds of bloody operations.

In Germany last year, a Pakistani man was sentenced to four years in prison for scouting out potential targets with links to Israel and Jewish organizations on behalf of the Quds Force, the external operations arm of Iran’s Revolutionary Guard Corps. According to court documents, he had been in touch with his Iranian handlers since at least 2011. But the “contact intensified” in the middle of 2015, around the same time that authorities believe the couple planning to attack the MEK rally were first contacted by Assadi.

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Officials said that Iran has recruited people from Pakistan, as well as from Iraq, Lebanon, Turkey, North Africa and Afghanistan, in order to obscure the country’s role in overseas spying.

A high-level German official said Iran’s aggression inside Europe calls for a tougher response.

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“There are clear indications for calling this a case of state terrorism,” the official said of the thwarted Paris attack. But leaders in Germany and France, the official said, “would rather play the danger and level of interference down,” in order to hold together the nuclear deal.

Norman Roule, who served 34 years in the CIA and retired last year as the national intelligence manager for Iran, said the lack of a tougher European response, especially in the wake of Iran’s support of terrorism on the continent, has likely sent a message to Tehran: “You can get away with pretty much anything.”

Roule said that Iran has been testing the limits of European and American resolve for decades. The regime has launched cyberattacks, supported terrorist groups, and, in 2013, plotted to kill the Saudi ambassador to the United States at a fashionable restaurant in Washington — an attack Roule said would probably have inflicted civilian casualties. All those events saw little tangible response, he said.

“My fear is that Iran may well believe they have yet to reach our red line, and this is a recipe for further attacks,” Roule said.

While U.S. officials have accused Iran’s top leaders of being behind the biggest plots, Iranian intelligence factions have sometimes acted in competition with one another, with little apparent coordination with the country’s ruling clerics, former U.S. officials said. Some think that pattern may be repeating now.

“It is not always the case that a senior [Iranian] official says, ‘Go and do this,’ ” said Matthew Levitt, a former counterterrorism official with the Treasury Department and the FBI. “Sometimes initiative — even stupid initiative, even initiative that fails — is smiled upon within this system.”

In light of the operations in Europe and the United States, it’s not clear that the Iranian leadership is in control of its own operatives, said intelligence officials in multiple countries.

One German official said that based on his government’s discussions with Iranian President Hassan Rouhani and Foreign Minister Mohammad Javad Zarif, Iran’s leaders understand that an attack in the heart of Europe could do irreparable damage to their country’s relationship with the remaining signatories to the nuclear deal.

But there is also a parallel power structure in Iran, and as domestic unrest grows and more Iranians die fighting in Iraq and Syria, Iranian hard-liners elsewhere in the government could push for a show of force against the West, the German official said.

The regime has also been humiliated by recent Israeli spying operations that laid bare huge troves of documents about Iran’s nuclear weapons program. Israeli Prime Minister Benjamin Netanyahu has publicly crowed about his spies’ prowess and has pressed for a tougher international response to Iran.

In a speech last month at the United Nations General Assembly, Netanyahu cited the arrest of the two operatives in the U.S. and the foiled Paris attack as evidence of Iran’s continued support of terrorism in the West, despite the election of more moderate leaders and the nuclear deal.

“If you think that Iran’s aggression has been confined to the Middle East, think again,” Netanyahu said.

An Israeli official said that there is a directive from the top levels of the Iranian government to develop targets quickly, and that the Intelligence Ministry has pushed its operatives to work too fast, leading to mistakes and arrests.

The two Iranian men arrested on suspicion of spying inside the United States were under surveillance by the FBI for an extended period of time, with their travel inside and outside the country tracked, according to a criminal complaint filed in the case.

The two men also appeared to be pressed for time. The alleged agent with dual Iranian and American citizenship urged his associate, who lived in California, to hand over photographs and other material he’d been gathering for target packages. But the California man “expressed some frustration,” according to the complaint, because he wanted more time to get the materials in order.

“I don’t like to do it this way . . . I like to have a complete package, meaning that there is no gap in information,” he said.