IN RECENT weeks the Obama administration has radiated optimism about the possibility of a deal with Iran on its nuclear program. The latest round of talks in Baghdad this week should lower those expectations. Tehran’s negotiators rejected a package offered by the United States and its five partners covering proposed confidence-building measures, and it demanded recognition of an Iranian “right” to enrich uranium, a concession U.S. officials say they are unprepared to make. The only substantive agreement was on holding another meeting next month in Moscow.

For now prolonging diplomacy serves both sides. Iran is able to continue its nuclear work: Reports based on recent international inspections say that it is continuing to add centrifuges to an underground facility called Fordow. The United States and its allies, meanwhile, can hope that the approaching implementation at the end of June of tough new sanctions — including a European embargo on Iranian oil — will provide more leverage. Both sides wish to head off a military strike by Israel, which is unlikely to act as long as talks continue.

Some U.S. patience is warranted. But extended negotiations will only benefit Iran, by allowing it to continue work on the Fordow underground facility, which may be nearly immune to Israeli military attack. What’s most concerning about the Baghdad talks is that they failed to show that the regime of Supreme Leader Ali Khamenei has made a strategic decision to strike a bargain. Instead, Tehran sought something for nothing: acceptance by the West of its uranium enrichment in return for assertions that it is not seeking nuclear weapons and promises to cooperate with international inspectors.

In fact no “right” to process uranium exists under the Nuclear Non-Proliferation Treaty, and multiple resolutions of the U.N. Security Council have ordered Iran to cease enrichment. The Obama administration rightly has taken the position that it will consider accepting Iranian uranium enrichment only at the end of a negotiating process; even then such a concession would be highly risky and probably unacceptable to Israel.

For now, the crucial question is whether even an interim, time-buying deal is possible. The administration’s optimism was based on the notion that Iran would agree to cease its most advanced form of uranium enrichment, export the stockpile of that material to the West and stop operations at Fordow in exchange for several Western concessions, like the supply of spare parts for commercial aircraft and fuel for a reactor that produces medical isotopes. In Baghdad, Iran rejected that deal as one-sided; it appears to expect major sanctions relief in exchange for any freeze of advanced enrichment.

That, too, must be unacceptable to the West. Sanctions are just beginning to seriously squeeze the Iranian regime, and they must remain in place until the threat posed by its nuclear activities has been eliminated. The chances of the Khamenei regime yielding to that extent remain remote. While an interim bargain that arrests what has looked like a slide toward war remains desirable, Iran cannot be granted much more time to build and install centrifuges. The next round of talks must be more productive.