Iran and the six world powers seeking to negotiate with it took a step back from confrontation Saturday when they reopened talks after an almost year and a half break. The discussions in Istanbul went well, both sides said, as they focused on the disputed Iranian nuclear program. The two sides agreed to meet again—in Baghdad on May 23.

It was a turning point at a time of increasing tensions with Iran over its alleged pursuit of nuclear weapons. This is true even though there was no agreement on measures to take and neither side made proposals. EU foreign policy representative Catherine Ashton, who speaks for the so-called P5 plus 1 negotiating team of Britain, China, France, Germany, Russia and the United States called the discussion “constructive and useful.” The word “constructive” was significant. The test of the talks had been to see if Iran, which claims its program is a drive to use the atom peacefully, would talk seriously about nuclear matters.

The idea was to get started on talks that had a chance of succeeding. Said Ashton: “We want now to move to a sustained process of serious dialogue, where we can take urgent practical steps to build confidence and lead on to compliance by Iran with all its international obligations.” This “step-by-step approach” with “reciprocity” of rewards for compliance is designed to “lead to concrete steps towards a comprehensive negotiated solution which restores international confidence in the exclusively peaceful nature of the Iranian nuclear program,” Ashton said in a final statement after the intense 10 hours of talks, during which Iran rejected a request for a bilateral meeting with US representative Undersecretary of State Wendy Sherman. Iranian negotiator Saeed Jalili did meet separately with the Russian envoy Deputy Foreign Minister Sergey Ryabkov.

The real work remains to be done in getting Iran to surrender strategic parts of its nuclear work in return for concessions from the US-led international community. These could include dropping sanctions designed to cripple Iran’s economy and helping Iran develop its civilian atomic program.

The talks were the first between the two sides since January 2011, also in Istanbul. That meeting had ended in disaster. Iran had said economic sanctions against it must be lifted and its right to enrich uranium, which can be fuel for civilian power reactors but also the explosive core of atom bombs, must be unconditionally accepted. The P5 plus 1 left in outrage, convinced Iran was sabotaging the talks. What followed was a growing escalation in tension and rhetoric as fears of an Israeli attack on Iran’s nuclear program rose. But in March, US President Obama convinced Israeli Prime Minister Benjamin Netanyahu at a summit in Washington to give diplomacy a chance. And so the new talks.

There was concern they could founder. But there has been a changed tone in Iran. Iranian Supreme Leader Ayatollah Ali Khameini greeted Obama’s words that diplomacy not war was on the agenda by saying they were “an exit from delusion.” It was one of the most positive comments he had made about the United States since the Islamic Revolution in 1979. The head of Iran’s Atomic Energy Organization, Ferydoon Abbasi, said Iran would cap uranium enrichment at 20 percent, enough to drive a reactor which makes medical isotopes, but not refined enough for nuclear weapons.

The message from the P5 plus 1 was that Iran “simply can’t continue using rhetoric instead of specific proposals,” the diplomat said.

Jalili, who had been strident, in 2011, struck a gentler tone this time. A diplomat who attended the meeting told me: “It was completely different from what was the case last time.” Jalili “talked real issues. We used almost all of our time to discuss the nuclear program.”

The diplomat said Jalili had gone into specifics, for instance on 20 percent enrichment which the United States fears as too close to weapon-grade and even on a swap of its own enriched uranium to get fuel for a research reactor in Tehran which makes medical isotopes. But both sides shied away from in-depth discussion since “that was not the purpose. The purpose was to see whether the Iranians are really serious about doing something, and they are,” the diplomat said.

He said the Iranians said clearly that they wanted sanctions against them lifted, particularly “unilateral sanctions,” which apparently referred to the tough oil and financial measures that are cutting into Iran’s ability to sell its oil and to do business internationally. Jalili did not lecture his negotiating adversaries, as he had in 2011. He “understood that some give and take must be done,” the diplomat said.

The message from the P5 plus 1 was that Iran “simply can’t continue using rhetoric instead of specific proposals,” the diplomat said.

Jalili, meanwhile, asserted Iran’s rights at a press conference after the meeting. “Pressure does not work,” he said, standing in front of a brightly colored poster that read “Nuclear energy for all; nuclear weapons for none” and had the pictures of five Iranian scientists who have been assassinated in what Iran claims are Israeli-U.S. covert operations. Jalili said Iran would not back off from enriching uranium as legal under the Nuclear Non-Proliferation Treaty. He said the 20 percent enriched uranium was needed for making medical isotopes “used for more than 800,000 patients in Iran ... We need 20 percent for our peaceful purposes and our own need.”

But he echoed Ashton in calling for a “sustainable process” to clear up nuclear questions. He said this should be based “on confidence-building measures which could attain the trust of Iranians.” He praised the P5 plus 1 for a “positive approach” and a step away from the “language of threats.”

A senior U.S. official also stressed the positive nature of the talks, but said Washington’s dual-track policy of applying pressure through sanctions while seeking talks would continue until Iran actually moved to rein in its nuclear program. The Istanbul meeting was to “test if there was a conducive environment for serious discussion.”

Now that must be tested, the official said.

“If you hear skepticism from me and wariness, we haven’t talked to the Iranians for 15 months. We have not seen them address the concerns of the international community,” the official said, and added that if the Iranians did do this, there would be “reciprocal actions,” an apparent reference to eventual relief from sanctions.

Ashton said experts would prepare an agenda for the Baghdad meeting that would focus on concrete moves to take. An indication of how delicate this remains is that a European diplomat told me that the burden of proof would still be on Iran and that it was up to the Iranians to propose what they were prepared to do.

But the P5 plus 1 are going to have to make clear their concerns, explain why they need to be answered and lay out an effective timeline for moving forward. There is opposition to Iran enriching uranium to 20 percent and expanding enrichment to the Fordow site, which is almost impregnable since under a mountain. Two smaller issues, perhaps easier for the Iranians to respond to, are applying the Additional Protocol for wider inspections and giving early notice of plans to build nuclear facilities.

If Iran is not just buying time, as some fear, the sustained process should have a start and this is a way to do it. Iran may propose measures that suit it better, finding a way to compromise even as it asserts its inalienable right to enrichment. And there is going to have to be reciprocity, as all P5 plus 1 members stressed, which could involve a pledge to freeze some sanctions once Iran has verifiably eliminated its 20 percent work, for instance.

In the end, the process has to have obligations on both sides and if each side holds the other's feet to the fire over meeting promises, there just might be a way forward to de-escalation rather than conflict.

This article originally appeared on The Daily Beast.