Despite years of scrutiny, Iran’s nuclear program is still surrounded by uncertainty. Tehran says it is merely seeking to diversify its energy supplies and apply nuclear technology to benign purposes such as the use of isotopes in medicine.

There is much to suggest otherwise. Time and time again, Iran has been forced to concede that it has hidden parts of its nuclear program, and has failed to give the International Atomic Energy Agency (IAEA), the world’s nuclear watchdog, the notice required for the construction of new facilities. Evidence has been found of a direct connection between Iran’s nuclear efforts and its military.

When offered a solution that would allow it to silence critics of its nuclear program, Iran has demurred, preferring to keep its options open. All the while, Tehran has been improving its capabilities in the most provocative manner.

Last October the international community, working through the IAEA, proposed that Iran export most of its low-enriched uranium and in return receive fuel rods suitable for use in a medical reactor. The export would ensure Iran does not have raw material that it could enrich to weapons-grade; the provision of the reactor-ready fuel would eliminate Iran’s need for enrichment capabilities that could be used to make a nuclear bomb.

After at first informally accepting the deal, Iran backed up, saying it would agree only to a swap on its own territory. It was not prepared to export the uranium as a first step. Iran continued to delay its official response to the proposal, holding out for better terms. In February, Tehran provided a formal counteroffer — and it looked a lot like the original deal it rejected. In the time since October, though, Iran has upped the ante, announcing that it has increased its uranium-enrichment capability to 20 percent and that it is planning to build 10 more enrichment facilities, two in the next year.

By all appearances, Iran is stalling for time as it seeks to develop the ability to sufficiently enrich uranium so that it can be used in a bomb, and to hone the engineering skills needed to put such a weapon on a missile. Iran appears to be betting that the rest of the world will remain divided on its intentions and that the United Nations Security Council will not impose sanctions, which it has the authority to do if the IAEA finds Iran to be in violation of its obligations. Thus far, that has been a safe bet. The odds may be changing, however.

Two countries have held out against imposing sanctions on Iran: Russia and China. Neither has been prepared to jeopardize its lucrative trade and business relations with Tehran, and both like the idea of the United States being either preoccupied with developments in Iran or humbled by Iranian intransigence. Washington’s need to win over Moscow and Beijing has also increased their leverage over the U.S. on other issues.

But Moscow’s patience may be exhausted. Last month, Russia said it was “very alarmed” by the possibility of Iran trying to build a nuclear weapon, and by Tehran’s ongoing refusal to cooperate with the IAEA. Foreign Minister Sergei Lavrov said Russia “cannot accept this.”

What triggered the change in Russian thinking? Credit the IAEA, and the first report on Iran’s nuclear program under its new director general, Mr. Yukiya Amano. Breaking with the language approved by his predecessor, the assessment concludes that “the information . . . raises concerns about the possible existence in Iran of past or current undisclosed activities related to the development of a nuclear payload for a missile.” While it does not claim outright that a program does in fact exist, it is much more direct and hard-hitting than earlier reports.

The shift in the IAEA’s tone makes it harder for sympathetic governments to side with Iran. But Moscow is also concerned because Tehran’s intransigence is helping Washington make the case for missile defense deployment on Russia’s periphery. That is a genuine strategic concern for Russia that outweighs the prospective benefits of “distracting” the U.S.

If Russia is ready to support another round of sanctions on Iran, then the pressure on China is doubled. While Beijing is always uncomfortable with international pressure being exerted on any country, it is even more troubled by the prospect of being the lone holdout at the United Nations Security Council. Russia’s shift denies China political cover. Iran’s room for maneuver has been considerably reduced.

The deal proposed to Iran is a good one. The world should accept Iran’s right to pursue peaceful uses of nuclear technology. Tehran does not need to enrich uranium to do that — and by agreeing to the deal, it will receive reactor-ready fuel and see sanctions lifted. It is a win-win solution and would be an important first step toward successful long-term diplomacy with Iran.

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