GENEVA — In the strongest sign yet that the first phase of a nuclear deal with Iran may be near, Secretary of State John Kerry arrived in Geneva on Friday, joining three of his international counterparts who also arrived unexpectedly: British Foreign Secretary William Hague, French Foreign Minister Laurent Fabius and German Foreign Minister Guido Westerwelle.
After his arrival, Kerry cautioned that "there is not an agreement at this point in time."
"I want to emphasize there are still some very important issues on the table that are unresolved. It is important for those to be properly, thoroughly addressed," he said. "We hope to try to narrow those differences, but I don't think anybody should mistake that there are some important gaps that have to be closed."
The sudden arrival of so many of the world's top officials sparked a high level of anticipation in Geneva, with increased security, including bomb-sniffing dogs, and an influx of the world's media.
The dignitaries are all expected to meet with Iran's Foreign Minister Javad Zarif. While the State Department says Kerry came to Geneva "in an effort to help narrow the differences in negotiations," it appears an initial agreement is virtually a done deal.
Negotiators worked late into the night Thursday night, in advance of Kerry's arrival. And both a senior U.S. official and Iran's foreign minister have said a deal could be signed Friday.
To be clear, this would only be the first step of a comprehensive nuclear deal still to be hammered out.
It would, however, be a significant step. While full details aren't yet known, a senior U.S. official said the deal would reign in advancements in Iran's nuclear program in return for a "limited" and "reversible" easing of economic sanctions.
Zarif told NBC News there will be political fallout in both Iran and the U.S., if this first step is indeed signed in the coming hours.
Already Israel's Prime Minister Benjamin Netanyahu, who has warned for years that Iran is close to having a bomb, is alarmed enough to call the deal being negotiated here "a historic mistake."
On Friday, he released a video expressing his strong feelings against the deal.
"Israel is not obliged by this agreement and Israel will do everything it needs to do to defend itself and the security of its people," Netanyahu told reporters after meeting with Kerry in Jerusalem.
President Barack Obama called Netanyahu Friday to discuss Iran, the White House said, and "underscored his strong commitment to preventing Iran from obtaining a nuclear weapon, which is the aim of the ongoing negotiations between the P5+1 and Iran."
Israel, which accuses Tehran of seeking to build atomic weapons, has repeatedly warned it might strike Iran if it doesn't halt its Iran hopes to get a break at the talks from crippling international sanctions that have caused its economy to collapse. The U.S. has said world powers will consider relaxing some sanctions if Iran takes visible steps to limit its nuclear program.
Israel has called for the sanctions to stay until Iran has dismantled its entire uranium enrichment program.
"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, Reuters reported.
President Obama said sanctions, which have been imposed since 2006, could be slightly eased in the early stages of negotiating a broad deal.
"There is the possibility of a phased agreement in which the first phase would be us ... halting any advances on their nuclear program ... and putting in place a way where we can provide them some very modest relief, but keeping the sanctions architecture in place," he said in an interview with NBC News' Chuck Todd.
Kerry flew to Geneva hours after meeting with Netanyahu. In Geneva, Iran and six world powers will hold negotiations: the five permanent members of the U.N. Security Council — the U.S., Russia, China, France and Britain — plus Germany.
From Israel, Kerry said Washington would not make a "bad deal, that leaves any of our friends or ourselves exposed to a nuclear weapons program," according to Reuters.
NBC's Elizabeth Chuck contributed to this report.