It is the latest sign of Iran's new pragmatic approach to the nuclear issue. Tehran is unlikely to ever completely stop enrichment. But by dropping a demand that makes no practical difference, it can move on to its most pressing concern; an easing of sanctions crippling its economy.
Less than two months ago, President Hassan Rouhani conditioned any agreement on recognition by the United States and its allies of such a right. But with both sides hoping to seal a deal at meetings that start Wednesday, Tehran tweaked its message Sunday.
Tehran's right of enrichment remains "nonnegotiable," Foreign Minister Mohammad Javad Zarif was quoted as saying by the semi-official ISNA news agency. "But (we) see no necessity for its recognition as a right."
Despite previous signs that Iran is ready to compromise under the moderate Rouhani, such a major shift is a surprise. Former U.S. State Department official Mark Fitzpatrick calls it a "very significant development, representing a key concession by Iran and a way to overcome a major hurdle to a deal."
It's unlikely that Rouhani acted without seeking approval from Iran's supreme leader, Ayatollah Ali Khamenei.
But the change is sure to add to concern among skeptics in Tehran fearful that Iran may be giving away too much for too little in return — and increase pressure on Iran's negotiators to show otherwise. Fitzpatrick, who now is a director at the International Institute for Strategic Studies, says he expects Iranian hard-liners "to raise hell about it."
Enrichment is a hot-button issue because it can be used both to make reactor fuel and to arm nuclear missiles. Iran argues it is enriching only for power, and scientific and medical purposes. And it says it has no interest in nuclear arms.
But Washington and its allies point to Tehran's earlier efforts to hide enrichment and allege it worked on developing such weapons.
Gary Samore, part of the U.S. negotiating team with Iran until earlier this year, describes the dispute over Iran's claimed right as being "at the heart of the nuclear negotiations for the past decade."
In an article for "Foreign Affairs," he says that with no court authorized to interpret the nuances of the 1970 nuclear Nonproliferation Treaty — which grants the right to nuclear power for peaceful purposes but doesn't specifically mention the right to enrichment — it will remain "impossible to resolve the legal question."
But even if squabbling over that issue is put aside for now, other differences may remain in the way to an initial agreement that freezes Iran's nuclear program in exchange for some relief of sanctions crippling Tehran's economy.
As a first step, the six want limits on Iran's overall capacity to enrich and a total stop to enrichment to a level that can be turned to weapons-grade uranium much more quickly than Iran's main stockpile of lower-enriched, fuel-grade material.
They also seek more rigorous international monitoring of Iran's nuclear facilities and some formula that eases international concerns about a reactor now under construction that will produce plutonium, which also can be used to arm a nuclear bomb.
Reflecting deepening rifts, the semiofficial Mehr news agency said Tuesday that some Iranian parliamentarians are working to block the government from agreeing to such concessions.
Iranian Foreign Ministry spokeswoman Marzieh Afkham, meanwhile, warned members of U.S. Congress favoring new sanctions that such a move would "completely destroy ... the healthy and useful atmosphere" at the talks.