WASHINGTON/PARIS (Reuters) - Nations that struck the 2015 Iran nuclear deal, except for the United States, meet on Monday in what many diplomats fear may prove a quixotic effort to keep the agreement alive after U.S. sanctions targeting Iranian oil exports resume in November.

Ministers from Britain, China, France, Germany, Russia and Iran will gather in New York at 8 p.m. EDT on Monday (0000 GMT Tuesday) to grapple with U.S. President Donald Trump’s May 8 decision to withdraw from the deal and restore the full force of U.S. sanctions on Iran.

Their delicate, and perhaps unrealistic, task is to build a case for Tehran to respect the deal’s limits on its nuclear program even though Washington has pulled out, depriving Iran of many of the economic benefits it was promised.

Iranian President Hassan Rouhani “needs arguments to defend the deal in the face of the radicals. He needs us to give him ammunition,” said a senior European diplomat, referring to Iranian hard-liners who oppose the agreement.

“We are trying to give him ammunition, but what we can do, to be honest, is limited,” the diplomat added.

The crux of the deal, negotiated over almost two years by the Obama administration, was that Iran would restrain its nuclear program in return for the relaxation of sanctions that had crippled its economy. Trump considered it flawed because it did not include curbs on ballistic missiles or regional activity.

The United States began reimposing economic sanctions this summer and the most draconian measures, which seek to force Iran’s major customers to stop buying its oil, resume Nov. 5.

FILE PHOTO: FILE PHOTO: An Iranian national flag flutters in Tehran April 15, 2011. REUTERS/STR/File PhotoREUTERS

Their impending return has contributed to a slide in Iran’s currency. The rial has lost about two-thirds of its value this year, hitting a record low against the U.S. dollar this month.

The European Union has implemented a law to shield European companies from U.S. sanctions. Still, there are limits to what it can do to counter the oil sanctions, under which Washington can cut off from the U.S. financial system any bank that facilitates an oil transaction with Iran.

“HURT THEM MORE THAN US”

Many European companies are withdrawing or have withdrawn from Iran because of U.S. sanctions that could cut them off from the American market if they stay.

Iran believes the United States acted in bad faith by withdrawing from the deal even as Tehran has adhered to its terms and has rejected U.S. overtures to meet.

The most recent confidential report by the International Atomic Energy Agency, the Vienna-based U.N. watchdog, found Iran had stayed within the main limitations imposed under the deal, whose formal name is the Joint Comprehensive Plan of Action (JCPOA).

In recent weeks, Iranian officials have begun arguing that if the Europeans cannot preserve trade with Iran, perhaps Tehran should reduce, but not eliminate, its compliance with the accord.

On Saturday, Iranian Foreign Minister Mohammed Javad Zarif was quoted as telling Germany’s Der Spiegel magazine that Iran could “reduce its implementation” and possibly increase uranium enrichment activities if the deal was jeopardized by “the actions of the Americans and the passivity of the Europeans.”

European diplomats wish to avoid this. Hoping to keep Iran’s nuclear program in check, they have told Tehran that if it stops carrying out the deal to the letter, they will have no choice but to restore their own sanctions.

“They keep telling us the situation is horrible, they are going to leave the accord or just keep partially implementing the deal. It’s the same old music, but for now they continue to implement the JCPOA,” said a second senior European diplomat.

“We (are) warning them that if they were to pull out it would hurt them more than us,” he added.