By Tom Cohen and Holly Yan

A breakthrough deal on Iran's nuclear program could be on the horizon - even though Western allies are splintered on the terms.

World leaders will meet Wednesday in Geneva, Switzerland, to discuss a proposed deal that would loosen economic sanctions against Tehran in exchange for a suspension of part of its nuclear program.

The Geneva talks involve Iran and the five permanent members of the U.N. Security Council - the United States, Russia, China, Great Britain and France - as well as Germany in what is known as the P5+1 in diplomatic shorthand.

U.S. National Security Adviser Susan Rice said the plan would benefit the global community.



"The international community would have unprecedented access to Iran's nuclear facilities and full transparency into what they're doing, so they wouldn't have the ability to sneak out or break out," Rice said.

But Israel, the United States' closest ally in the region, staunchly opposes the tentative plan.

"It's a bad deal - an exceedingly bad deal," Israeli Prime Minister Benjamin Netanyahu told CNN this week.

Netanyahu opposes lifting some sanctions now without getting further concessions to ensure Iran would be unable to continue with uranium enrichment and other steps.

"I think you should not only keep up the pressure; I think you should increase the pressure, because it's finally working," Netanyahu said, labeling Iran's economy as close to paralysis. "If you give it up now, when you have that pressure, and Iran doesn't even take apart, dismantle one centrifuge, what leverage will you have when you've eased the pressure?"

At the same time, Netanyahu repeated his insistence that Israel "always reserves the right to defend itself against any threat," which is diplomat-speak for a military strike on Iran's nuclear facilities to stop development of a weapon.

Iran: Israelis 'are like animals'

The Supreme Leader of Iran, Ayatollah Ali Khamenei, didn't mince words when he fired back at Israel.

"Israeli officials cannot be even called humans. They are like animals, some of them," Khamenei said Wednesday.

The ayatollah also said Iran's "heroic flexibility" is not a violation of Iran's values. Khamenei coined that term a few months ago to explain that Iran's leadership can be flexible while remaining "heroic" in the face of Western powers it still doesn't trust.

Rifts within the U.S.

Even some U.S. lawmakers aren't sold by the new plan. On Tuesday, a bipartisan group of six senators urged the administration to reject the proposed deal with Iran and only accept an agreement that better dismantles Iran's ability to develop nuclear weapons.

"I think all of us are concerned," said Republican Sen. Bob Corker of Tennessee. "We know who we are dealing with, and we've watched this same type of activity occur in North Korea, where you began to alleviate sanctions, and I think what the concern is that whatever you do in the interim basis becomes the new norm."

But U.S. President Barack Obama said the current sanctions put in place during his administration had forced Iran to the negotiating table because of economic contraction and frozen oil revenue.

He said the proposed deal would "open up the spigot a little bit" on some of the frozen revenue while leaving in place the bulk of the most effective sanctions involving Iranian oil exports and banking. But Obama also stressed that all options, including military strikes on Iran's nuclear facilities, remained on the table as far as the United States was concerned.

According to a senior U.S. administration official, the talks are "getting close" to an interim deal with Iran that would prevent its nuclear program "from advancing, and roll it back" in key areas. The last round of negotiations broke up without a deal earlier this month, with each side blaming the other's reluctance.

CNN's Jim Sciutto, Saad Abedine and Reza Sayah contributed to this report.