With President Trump and Iranian leaders slinging insults at each other, Europe is diving into a lightning round of diplomacy to rescue the faltering Iran nuclear deal and avert a further escalation of conflict. But European leaders are bumping up against the limits of what they can do without provoking their own fight with Trump.

“It’s a very narrow path for Europeans to walk,” said Nathalie Tocci, an adviser to E.U. foreign policy chief Federica Mogherini. “Ultimately, you’re doing something very small, and at the same time this triggers the ire of your greatest ally at a time of tremendous tensions.”

The Europeans have found themselves unable to blunt U.S. sanctions or aggressive rhetoric.

They have tried to set up a system that could facilitate some trade with Iran, but that plan has been bogged down in technical delays. Meanwhile, few European companies have been willing to expose themselves to the secondary sanctions that could come with continuing to do business with Iran.

Europeans were relieved that Trump called off retaliatory airstrikes on Iran last week after Tehran shot down a U.S. drone. But they are worried that the U.S. president and Iranian leaders could still bluster their way into war.

“We’re not out of the cycle,” Tocci said. “The risk of an accidental war is sky-high. And a reaction — now the U.S. reaction to a reaction to a reaction, this is the cycle that we’re in — is likely to trigger some sort of Iranian reaction.”

French President Emmanuel Macron wanted to lobby Trump at a summit in Japan this week to dial down tensions. Instead, Macron had trouble even getting a meeting with the U.S. leader.

The Europeans have also struggled to hold back Iranian hard-liners who are pushing for a departure from the 2015 nuclear deal. Top European diplomats have cycled through Tehran in recent days in a show of commitment to the accord. Still, Iranian Ambassador to the United Nations Majid Takht Ravanchi told a Security Council meeting Wednesday that Iran would break limits on low-enriched uranium unless Europe did more to save the nuclear agreement.

Iran’s ambassador to the United Nations, Majid Takht Ravanchi, delivered a warning to the Security Council. (Spencer Platt/Getty Images)

Europe and the United States would have to “accept the full responsibility for any possible consequences,” he said.

Until now — even after Trump announced the U.S. withdrawal from the deal in May 2018 — Iran has held to the agreement, which tightly restricts the amount of nuclear materials it is allowed to produce and possess.

Senior diplomats representing the remaining signatories — Iran, China, Russia, Britain, France, Germany and the European Union — will meet in Vienna on Friday. They will talk about Iran’s nuclear stockpile and hear from representatives of the International Atomic Energy Agency, which is charged with monitoring Iran’s compliance with the deal. The Europeans are not sure yet whether they will meet to deliver an elegy to the deal or whether the agreement, on life support, will struggle on.

If Iran does breach some limits in the coming days but does not appear to turn irreversibly away from the deal, Europe may temper its pushback, diplomats said. But they warned that an Iranian violation would complicate their efforts to extend a diplomatic hand to Tehran.

The desire to keep Trump’s anger about Iran from crossing over into frustration with NATO may explain why alliance defense ministers were so resolute during meetings Wednesday and Thursday about leaving the Iran file to others. Diplomats expected to hear about Iran from acting U.S. defense secretary Mark Esper, but not in detail.

Acting U.S. defense secretary Mark Esper made his international debut at a NATO meeting in Brussels this week. (Aris Oikonomou/AFP/Getty Images)

Instead, the defense ministers held firm to their somewhat eclectic original agenda: a consideration of establishing a new NATO focus in space, a discussion of the role of artificial intelligence in defense and the latest plans to deal with Russia.

Meanwhile, Trump continued to issue angry rhetoric about Iran.

“I’m not talking boots on the ground. I'm just saying if something would happen, it wouldn’t last very long,” Trump told Fox Business on Wednesday as defense ministers gathered in Brussels.

One defense minister tried to defuse the issue with a gentle joke.

“He’s also said he doesn’t want war with Iran, and I like that statement better,” said Norwegian Defense Minister Frank Bakke-Jensen. “The danger of an escalation is very high.”

Europe’s muted role in rescuing the deal has frustrated some politicians.

“The Europeans have not done enough to defuse the situation,” said Omid Nouripour, the foreign affairs spokesman for Germany’s opposition Green Party, calling for more money to bolster efforts to defy the sanctions.

Europeans say they may not be able to do much to save the nuclear deal. But if they have a role, it will be through the trade tool they have been trying to set up with Iran since Trump announced that the United States would reimpose crushing sanctions.

The Instrument in Support of Trade Exchanges, or Instex, is as complicated as its name. So complicated that it has not yet yielded any transactions. Europeans acknowledge that the tool, which would facilitate a kind of barter for humanitarian goods, will not do much for Iran’s gasping economy. But they say they hope to sell it as a symbol of their good faith regarding the nuclear deal.

“This is now ready to be operational, and I hope that this is something that can help to keep Iran compliant with the agreement,” Mogherini told reporters Tuesday. She said Europe was working to save the deal under “probably the most difficult conditions you could imagine.”

But Iran has grown increasingly frustrated — especially after the United States in May tightened sanctions on Iran’s oil exports. The lack of revenue is asphyxiating Iran’s economy, empowering hard-liners who have long opposed the deal.

“Iran has essentially told Europe: You’re actually not doing anything,” said Michal Koran, the president of the board of the Global Arena Research Institute, a Prague-based think tank.

One senior European diplomat, speaking on the condition of anonymity to discuss sensitive considerations about the negotiations, said Europe would have difficulty proceeding with a first transaction through the new tool if Iran had just violated the deal. But if no support from Europe is forthcoming, Iran is likely to keep moving further away from compliance, the diplomat said.

“I’m afraid the Europeans are going to keep having to buy time with the Iranians,” said Ellie Geranmayeh, an Iran expert at the European Council on Foreign Relations. “We’re now at a stage where both the European influence and leverage both with Tehran and Washington is fairly limited.”

Noack reported from Berlin.