Updated at 3:08 a.m. Eastern
GENEVA U.S. Secretary of State John Kerry warned Friday of significant differences between , as he and three European foreign ministers added their weight to try to narrow the gap. But Russia expressed optimism about a deal.
Officials had reported progress in Thursday's talks. But comments from Kerry and his counterparts from Britain, France and Germany after they arrived in Geneva clearly indicated that obstacles remain in the way of any agreement offering sanctions reductions for nuclear concessions.
Russian news agencies reported late Friday that Russian Foreign Minister Sergey Lavrov would join Kerry and the European ministers in Geneva on Saturday.
Earlier Friday, Foreign Ministry spokesman Alexander Lukashevich had said Lavrov would not attend the talks.
Iran considers Russia most receptive to its arguments among the six world powers. For that reason, Lavrov's presence would add additional muscle to efforts to seal a preliminary deal that the West hopes will culminate with serious constraints on Iran's ability to turn a peaceful nuclear program into making weapons.
Reporting Lavrov's pending arrival, Russia's RIA Novosti news agency quoted Deputy Foreign Minister Sergei Ryabkov as saying Russia expects that the talks will produce a "lasting result expected by the international community."
The Russian statement suggested a possible narrowing of differences, hours after Kerry met first with his European counterparts, then with Iranian Foreign Minister Mohammad Javad Zarif and Catherline Ashton, the EU's top diplomat who convened the talks.
CBS News correspondent Elizabeth Palmer told "CBS This Morning" that while surprisingly few leaks about the details of the negotiations have emerged, expectations were high in Geneva that something could be announced by the weekend.
"This is not the great big omnibus deal that would lift all sanctions on Iran," explained Palmer. "This is a first step," she said, and the purpose would be to build trust so that the negotiations on that much broader deal can begin. "The goal is to reach the starting line, if you like, of that next chapter."
during which he tried to defuse Israeli concerns about the Geneva talks. Israel strongly opposes any deal that even slightly lifts sanctions unless Iran is totally stripped of technology that can make nuclear arms.
The talks primarily focus on the size and output of Iran's enrichment program, which can create both reactor fuel and weapons-grade material suitable for a nuclear bomb. Iran insists it is pursuing only nuclear energy, medical treatments and research, but the United States and its allies fear that Iran could turn this material into the fissile core of nuclear warheads.
Kerry said there were "some very important issues on the table that are unresolved."
"There is not an agreement at this point in time," he told reporters.
In earlier comments to Israeli television, Kerry suggested Washington was looking for an Iranian commitment to stop any expansion of nuclear activities that could be used to make weapons, as a first step.
"We are asking them to step up and provide a complete freeze over where they are today," Kerry said Thursday.
Six powers - the negotiators also include Russia and China - are considering a gradual rollback of sanctions that have crippled Iran's economy. In exchange they demand initial curbs on Iran's nuclear program, including a cap on enrichment to a level that can be turned quickly to weapons use.
The six have discussed ending a freeze on up to $50 billion (37 billion euros) in overseas accounts and lifting restrictions on petrochemicals, gold and other precious metals. But their proposal would maintain core sanctions on Iran's oil exports and financial sector, as an incentive for Iran to work toward a comprehensive and permanent nuclear accord.
Tehran could be pressing for more significant relief from the sanctions as part of any first-step deal. Iran's Mehr news agency quoted Iranian delegation member Majid Takht-e Ravanchi as saying his country was asking for an end to sanctions on oil and international banking transactions crippling the ability to repatriate money from oil sales.
French Foreign Minister Laurent Fabius, the first to arrive at the talks, spoke of progress, but told reporters "nothing is hard and fast yet."
"I've come to Geneva to take part in the negotiations because the talks are difficult but important for regional and international security," he said. "We are working to reach an accord which completes the first step to respond to Iran's nuclear program."
Israel has been watching the talks warily from the sidelines. It has frequently dangled the prospect of military action against Iran should negotiations fail to reach the deal it seeks - a total shutdown of uranium enrichment and other nuclear programs Tehran says are peaceful but which could technically be turned toward weapons.
"I understand the Iranians are walking around very satisfied in Geneva as well they should because they got everything and paid nothing," Netanyahu told reporters before meeting Kerry in Tel Aviv.
Earlier Friday, Netanyahu said that he "utterly rejects" the emerging nuclear deal between western powers and Iran, calling it a "bad deal" and promising that Israel will do everything it needs to do to defend itself.
Asked about Netanyahu's criticism, White House spokesman Josh Earnest said "any critique of the deal is premature" because an agreement has not been reached.
He added: "The United States and Israel are in complete agreement about the need to prevent Iran from obtaining a nuclear weapon."
Any agreement would be a breakthrough after nearly a decade of mostly inconclusive talks, but would only be the start of a long process to reduce Iran's potential nuclear threat, with no guarantee of ultimate success.
Tehran's chief nuclear negotiator, Abbas Araghchi, told Iranian state TV on Thursday that the six "clearly said that they accept the proposed framework by Iran." He later told CNN that he thinks negotiators at the table are now ready to start drafting an accord that outlines specific steps to be taken.
Though Araghchi described the negotiations as "very difficult," he told Iranian state TV that he expected agreement on details by Friday, the last scheduled round of the current talks.
White House spokesman Jay Carney said an initial agreement would "address Iran's most advanced nuclear activities; increase transparency so Iran will not be able to use the cover of talks to advance its program; and create time and space as we negotiate a comprehensive agreement."