Secretary of State John F. Kerry arrived in Geneva on Saturday to give a boost to stalled nuclear talks with Iran, raising hopes that a historic deal could be within reach.

The top U.S. diplomat flew to the Swiss city overnight and began a series of meetings with Russian and European counterparts who also traveled here to try to salvage an agreement on scaling back Iran’s nuclear program.

Kerry decided to intervene in the talks for a second time in two weeks after negotiators reportedly made progress in overcoming key obstacles to a deal. It was hoped that Kerry’s personal diplomacy could helps the sides “narrow the differences and move closer to an agreement,” State Department spokeswoman Jen Psaki said in a statement announcing the visit.

Kerry joined Russian Foreign Minister Sergei Lavrov, who arrived in Geneva on Friday, as well as British and French counterparts who traveled to Switzerland early Saturday. Diplomats and technical teams from Iran and six major powers had been meeting privately since Wednesday to resolve a number of sticking points, including Iran’s insistence on international recognition of its “right” to enrich uranium.

State Department officials cautioned that Kerry’s decision to attend the talks did not necessarily portend an imminent agreement.

“These are tough and challenging negotiations,” Psaki said. “It’s not easy to get to the finish line. And as the secretary has said many times, he is the last person who is going to accept a bad deal.”

But she added that negotiators appeared to be “closer than we’ve ever been in a decade to achieving a diplomatic agreement for a first step with the Iranians.”

Britain’s foreign secretary, William Hague, announced that he would also join the talks Saturday.

The proposal being hammered out in Geneva would require Iran to halt or scale back key parts of its nuclear program in return for what U.S. officials have described as modest, temporary relief from some of the economic sanctions that have crippled Iran’s economy. The plan is intended to essentially freeze Iran’s nuclear expansion while diplomats attempt to negotiate a more comprehensive agreement setting permanent limits on Iran’s ability to produce nuclear weapons. Iran insists that its nuclear facilities are intended only for energy production.

The news of Kerry’s impending arrival capped a day in which prospects for a deal appeared to brighten appreciably. Iranian officials, who had given generally gloomy assessments of the talks earlier in the week, were visibly upbeat as the meetings dragged on. Iranian news media reported that progress had been made on one of the main points of contention: Iran’s insistence that global powers acknowledge its “right” to make enriched uranium. Western diplomats declined to comment on the report.

“If you’re asking about the amount of work that has been done, we have moved forward up to 90 percent,” Iranian Foreign Minister Mohammad Javad Zarif told Iranian journalists during a break in the talks, according to Iran’s semiofficial Press TV news service. Zarif said only “one or two issues” remained to be resolved.

On the key issue of uranium enrichment, Zarif said making the nuclear fuel for Iranian power plants was “a right that Iran will not withdraw from.”

“The Islamic republic’s enrichment program will be a major part in any solution and any negotiation,” Zarif said.

U.S. diplomats have described efforts to find language that would satisfy Iran without implying legal recognition of a right
to enrichment. Under the Non-
Proliferation Treaty, member states are allowed to pursue nuclear energy for peaceful purposes, though the treaty is silent on whether that right includes uranium enrichment. More than a dozen countries enrich uranium for nuclear power, including ­non-nuclear weapons states such as Brazil, Japan and the Netherlands.

The Geneva meeting is the third round of international talks on Iran’s nuclear program since moderate cleric Hassan Rouhani assumed the presidency in August. The sides fell just short of reaching an agreement at the last round, two weeks ago, when Kerry and his counterparts from Europe and Russia flew to Geneva at the eleventh hour to try to close the deal.

In Washington, Obama administration officials expressed cautious optimism for an agreement in Geneva. White House spokesman Jay Carney said U.S. diplomats were in lockstep with their European, Russian and Chinese counterparts, the other members of the negotiating bloc known as the P5+1.

“We remain hopeful that we can reach an agreement with all of our P5+1 allies and the Iranians in Geneva,” Carney said.

As the Iran talks were progressing, the United States, Iran, Russia, Saudi Arabia and other key regional and international powers held informal discussions Thursday in Geneva to devise a strategy for improving the United Nations’ stalled relief effort in Syria, according to diplomatic sources familiar with the effort.

The meeting — held at the French mission to the United Nations in Geneva — was convened to lay the groundwork for a more formal U.N.-sponsored meeting scheduled for Nov. 26 in Geneva on the future of international relief efforts in Syria.

The participation of American and Iranian officials provided further evidence that the decades-long diplomatic freeze was beginning to thaw, offering new areas beyond the latest round of nuclear diplomacy where the longtime enemies can cooperate.

The U.N. emergency relief coordinator, Valerie Amos, organized the session to bring together key regional and outside powers with influence on the warring parties and a willingness to prod them to provide greater access to international relief workers. Together, she hopes, they can prevail upon Syria and the armed opposition to comply with an Oct. 2 statement from the U.N. Security Council that condemns “all cases of denial of humanitarian access” and calls for the facilitation of the “safe and unhindered delivery of humanitarian assistance in the whole country.”

Colum Lynch in New York contributed to this report.