Iran Demands Legal Pledge That U.S. Won’t Quit Nuclear Deal Again

The U.S. has consistently said no president can legally tie the hands of a successor without a treaty that would need to garner the backing of two thirds of the U.S. Senate. The U.S. has also said the current talks should remain focused on restoring the 2015 deal, not seeking new commitments on both sides.

The standoff over guarantees comes amid what U.S. and European officials say are signs of progress in the Vienna talks, involving Iran, the U.S., Britain, France, Germany, Russia and China. The 2015 deal suspended most international sanctions on Iran in exchange for tight but temporary restrictions on Iran’s nuclear program.

Western diplomats say a pathway to a deal is possible, showing more optimism since December when Iran’s demands left negotiations on the brink of failure. U.S. and European officials are privately eyeing mid-February as the moment to decide whether the diplomacy is exhausted.

There has been progress on the fine print, including how sanctions would be lifted, how Iran will scale back its nuclear work, and how a deal might be implemented over several months.

However, Western diplomats warn that a range of core political decisions on sanctions, nuclear steps and sequencing of an agreement must still be made and many worry whether Tehran is willing to cut a deal quickly enough. Western officials have repeatedly warned that the window for talks is closing given the advances in Iran’s nuclear work.

“This negotiation is advancing way too slowly to be able to reach a conclusion,” French Foreign Minister Jean-Yves Le Drian said Friday.

Saeed Khatibzadeh, a spokesman with Iran’s foreign ministry, said Monday that diplomats were making progress in Vienna but key issues remained that “require certain political decisions.”

“Washington should announce its decisions regarding the remaining issues and lifting of the sanctions,” he said.

By demanding an ironclad U.S. commitment to a deal, Iran’s concerns highlight a key weakness in the 2015 agreement. The deal was never signed as a treaty with clear legal guarantees. Its formal name—the Joint Comprehensive Plan of Action—underscored this was a set of political commitments, albeit pledges that were later backed up by a U.N. Security Council resolution.

Last spring, when talks to restore the deal started, Iran put a U.S. pledge not to leave the deal again on its wish-list, alongside other demands such as compensation for Washington’s 2018 withdrawal. Western diplomats felt that was largely for domestic show and that Iran would likely scale down its requests.

Last spring, under the previous Iranian government, Tehran did modify its position—saying it wanted a guarantee that Washington would stay in the deal as long as President Biden was in office. The new team, under President Ebrahim Raisi, has gone back to the original permanent guarantee demand.

In recent weeks, Western diplomats say they have started to see the demand for guarantees as a crucial objective for Mr. Raisi’s negotiators. Mr. Raisi is considered a possible successor to Iran’s Supreme Leader Ayatollah Ali Khamenei, who himself has demanded guarantees.

Ensuring that Mr. Khamenei isn’t again embarrassed by a future U.S. pullout appears to be a top political goal, two Western diplomats said.

“Absent guarantees, many in Tehran worry, sanctions relief will be ineffective, unsustainable and perhaps even detrimental to the Iranian economy as the specter of reimposed sanctions haunts long-term planning,” said Ali Vaez, director of Iran Project at Crisis Group, in a report published Monday.

In recent months, Washington has started to respond to Iran’s concerns.

On Nov. 1, on the sidelines of the Group of 20 nations in Rome, Mr. Biden and the British, French and German leaders issued a statement that was designed to address Iran’s concern head-on, diplomats say.

“In this spirit, we welcome President Biden’s clearly demonstrated commitment to return the U.S. to full compliance with the JCPOA and to stay in full compliance, so long as Iran does the same,” the leaders said.

Yet Iran has dismissed verbal pledges. A problem, Western diplomats say, is that Iran has at different times sought different types of assurances from Washington—political, economic and legal. Also complicating a solution: Iran refuses to negotiate directly with the U.S.

U.S. and European officials say they are exploring ideas to put to Iran which could generate additional confidence. Ideas that are being weighed are promises of letters of assurance from the U.S. Treasury Department for an agreed list of international banks and companies or a political commitment to some kind of phase-in of future sanctions. Yet these would fall short of ironclad, legal guarantees.

”Basically, there are proposals on the table on how economic operators can get some comfort if a new American administration reimposes sanctions,” said a person close to the talks. “In a democratic country, in three years time, [there] can be a new president and things can change. So we are working on that but there are no real magic ideas.”

Write to Laurence Norman at laurence.norman@wsj.com