US Secretary of State John Kerry joined European and Iranian officials in Geneva on Friday to continue negotiations on Iran's nuclear program, as talks were extended into Saturday.
Kerry's last-minute trip initially suggested a nuclear deal between Iran and six other countries could be reached as soon as Friday.
However, upon arrival Kerry re-iterated that there was no nuclear deal yet.
"I want to emphasize there are still some very important issues on the table that are unresolved," he said.
Israel's Prime Minister Benjamin Netanyahu did not wait for a deal to be announced to voice his opposition to it.
"I understand that the Iranians are walking around very satisfied in Geneva; as well they should be, because they got everything and paid nothing," Netanyahu said Friday, reacting to reports that Iran was being offered some sanctions relief. "So Iran got the deal of the century, and the international community got a bad deal; this is a very bad deal. Israel utterly rejects it."
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"Any critique of the deal is premature," White House spokesman Josh Earnest told reporters traveling with President Barack Obama on Air Force One to New Orleans on Friday. "There is no deal, but there is an opportunity here for a possible diplomatic solution, and that is exactly what the president is pursuing."
The White House issued a statement noting that Obama had telephoned Netanyahu on Friday to discuss the negotiations.
"The president provided the prime minister with an update on negotiations in Geneva and underscored his strong commitment to preventing Iran from obtaining a nuclear weapon, which is the aim of the ongoing negotiations," the White House said.
Kerry was expected to meet with Iranian Foreign Minister Mohammad Javad Zarif and make a joint statement, the Associated Press reported. He also met fellow ministers of the so-called P5+1 nations — the United States, Britain, China, France, Russia and Germany.
On Friday evening, Zarif told CNN's Christiane Amanpour, "We are prepared to address some of the most immediate concerns that have been raised, and we expect reciprocally our concerns to be met by the P5+1."
Nuclear talks between Iran and the P5+1 resumed in Geneva on Thursday morning.
Significant progress was reported throughout the day.
In another sign that a deal could be in the offing, Russian media said Foreign Minister Sergei Lavrov was on his way to Geneva. Lavrov, along with China's foreign minister, were expected to arrive in Geneva on Saturday.
State-run RIA news agency quoted Russia's main negotiator, Sergei Ryabkov, saying, "There are many issues affecting the deep-seated interests of several countries. That is why the level (of the talks) is becoming ministerial."
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A deal would be historic — the first in 35 years of strained US relations with Iran, according to NBC News.
Earlier, a senior American official and Zarif both said a deal could be reached Friday.
Zarif told NBC News "a piece of paper" could be signed Friday to seal a "first step" deal.
Under such an agreement, Iran would freeze most of its nuclear program for six months. In exchange, the country would be given partial, temporary and reversible relief from international sanctions.