Wednesday's first meeting of the full group was only 45 minutes long, but officials say that was the plan, and bilateral meetings were to continue well into the night.

　　This is the third time in five weeks that the negotiators from Iran's new government and the six-nation contact group have met.

　　Last time, Iranian Foreign Minister Mohammad Javad Zarif criticized the U.N. negotiators for changing course, a move widely attributed to French insistence on some key points. But during a stop in Italy on his way here, Zarif expressed optimism for this round.

　　“I go to Geneva with the determination to come out with an agreement at the end of this round," he said. "I'm sure that, with the necessary political will, we can certainly make progress and even reach an agreement.”

　　But Iran's Supreme Leader Ayatollah Ali Khamenei caused some concern in a speech on Wednesday, saying Iran “will not step back one iota” from what he called its “rights,” an apparent reference to its claim to a right to enrich uranium, which the United States says does not exist for any country.

　　In an Internet video released on Tuesday, however, Zarif had a line that gave some analysts hope for a solution to that dispute.

　　“Rights are not granted," he said. "Since they are not granted, they cannot be seized.”

　　That could imply that Iran will not insist on an explicit acknowledgment of a right to enrich, as long as any agreement does not prevent it from enriching. And a senior U.S. official in Geneva says negotiators can “navigate” the issue.

　　Middle East analyst Alison Baily at the British consulting firm Oxford Analytica says Iran's new government needs sanctions relief to fulfill its campaign promises, but it has to be careful.

　　“It cannot be seen to cave in to pressure from the international community," she said. "So it has to really find a formula which allows it to roll back sanctions but at the same time save face.”

　　Uranium enrichment is important for generating power and for medical research, two things Iran says it wants to do with its nuclear program. But taken to the extreme, enrichment can create weapons-grade uranium. Iran has come close to producing that, and built extensive, secure and previously secret enrichment facilities, raising fears it wants to build a nuclear bomb, although Iranian officials say they have no such intention.

　　Those fears resulted in severe international economic sanctions intended to convince Iran's government to negotiate an end to that part of its nuclear program, and allow inspections to prove it. The hardship caused by the sanctions was a key issue in June, when Iranian voters elected the relatively moderate government that is now pursuing negotiations.

　　The immediate goal is a first-stage accord that officials say would freeze Iran's program, and roll back parts of it, in return for limited sanctions relief. That would probably involve the release of some Iranian money held in international banks, but not any easing of trade embargoes or banking restrictions.

　　Then, negotiations would begin, on an expected six-month timetable, to try to reach a full agreement to verifiably limit Iran's nuclear program and gradually end all sanctions.

　　If the negotiations fail, there is a danger that Iran will come so close to being able to build a nuclear bomb that the United States or Israel will decide to take military action to prevent the final steps.

　　But that could trigger a regional war, and experts say would only delay Iran's program, not end it.

　　This week's talks involve the Iranian foreign minister and the European Union's foreign policy chief, along with senior officials of Germany and the five permanent members of the U.N. Security Council — the United States, Britain, France, Russia and China.