A grueling day of talks Wednesday between senior American, Iranian and European diplomats produced no breakthrough agreement on curbing Iran’s nuclear program, but officials said they still aim to reach a deal by the Nov. 24 deadline.

Secretary of State John F. Kerry, Iranian Foreign Minister Mohammad Javad Zarif and European Union foreign policy chief Catherine Ashton met for a total of six hours stretching through most of the afternoon and late into the night at an exclusive hotel in the center of Vienna.

A senior State Department official characterized each step of progress in the talks as “chipping away” at complex, technical differences, with virtually every sentence requiring an appendix of further explanation.

“We continue to make progress, but there is still a substantial amount of work to be done,” said the official, who spoke on the condition of anonymity to discuss the difficult and secretive negotiations.

The official declined to quantify how many issues were still on the table but said gaps remain to some degree in nearly all of them. Still, the official said it is premature to even discuss extending the November deadline.

Secretary of State John F. Kerry arrives at a hotel in Vienna for a meeting Wednesday with E.U. foreign policy chief Catherine Ashton and Iranian Foreign Minister Mohammad Javad Zarif. (Leonhard Foeger/Reuters)

“We hope Iran decides to take advantage of this historic opportunity,” the official said.

“We can foresee a way forward through a verifiable agreement that both resolves the international community’s concerns about . . . Iran’s nuclear program,” the official added, “and also provides the Iranian people with more economic opportunity and an end to isolation.”

A lot is at stake in the talks, which seek to rein in Iran’s nuclear capacity in exchange for an easing of economic sanctions on the country. Failure to craft a comprehensive deal could further destabilize the tumultuous Middle East and lead to a regional nuclear arms race.

Iran insists it has the right to expand its nuclear capacity, which it says it is using for peaceful purposes such as energy. But many in the West fear that Iran aims to use enriched uranium to make nuclear weapons.

The United States and other nations have been trying to get Iran to scale back its nuclear program for a decade, and the U.N. Security Council has passed six resolutions calling on Iran to stop enriching uranium. The five permanent members of the Security Council — the United States, Russia, China, France and Britain — along with Germany, have held several rounds of negotiations with Iran. But they did not progress much, and Iran has continued to enrich uranium.

Hopes that the talks might now succeed picked up last year after Iran elected a moderate president, Hassan Rouhani. An interim deal was reached, and the negotiators continued the talks in a bid to reach a comprehensive agreement, extending a July deadline to Nov. 24.

The talks have centered on technical issues that require nuclear experts to advise the negotiators. For example, the two sides still have not agreed on the number of allowed centrifuges, which can be used to enrich uranium. Iran reportedly has offered to freeze the ones already in operation, but the big powers want the number reduced. They are, however, not asking Iran to eliminate its nuclear program.

“We never would have gotten to this point if we didn’t agree to a limited domestic enrichment program, very carefully monitored,” said another U.S. official, who also spoke on the condition of anonymity, citing State Department protocol.

Administration officials have been trying to help Iranians envision their lives without sanctions, which have been imposed by the United States, the E.U. and the United Nations. In an interview last month with the Voice of America’s Persian-language service, Wendy Sherman, the chief U.S. negotiator, said some major sanctions would be suspended soon after an agreement was reached and predicted that “the world will flood into Iran.”

Even with a fast-approaching deadline, U.S. officials said the remaining issues can be settled in the next 51 / 2 weeks.

“There are a lot of ways to get to yes here,” the second U.S. official said.

Domestic politics, both in the United States and Iran, are adding to the sense of urgency. Some Republicans have openly opposed lifting sanctions, so if they gain control of the Senate in the upcoming midterm elections, it may be more difficult to get the votes needed for a deal. Iranian hard-liners have objected to concessions, and the position of Ayatollah Ali Khamenei, the country’s supreme leader, has been vague.

But Rouhani sounded an optimistic note when talking Wednesday on state television: “We think that the rest of the matters will be resolved in the next 40 days and can be ended.”

Still others are suggesting that an extension is inevitable and preferable to breaking off the talks at some self-imposed deadline. Russian Foreign Minister Sergei Lavrov, who met with Kerry on Monday in Paris, said there is nothing “sacred” about the November deadline.

Zarif said there were “serious and innovative” new proposals — which he did not specify — that required time to discuss.

Kerry, when asked Tuesday about the deadline in Paris, said an agreement was possible but declined to predict success.

“I don’t believe it’s out of reach, but we have some tough issues to resolve,” he said.