Israel has warned relentlessly against a nuclear deal with Iran, but experts say Prime Minister Benjamin Netanyahu's options are limited and immediate military action is unlikely.

Netanyahu slammed Thursday's announcement in Lausanne on the framework of a potentially historic deal, saying that if implemented it would jeopardise the Jewish state's very existence.

"PM Netanyahu to Pres Obama: A deal based on this framework would threaten the survival of Israel," Netanyahu spokesman Mark Regev wrote on his official Twitter account, quoting a late night telephone conversation.

Regev quoted the premier as saying that the deal as it appears to be emerging "would not block Iran's path to the bomb. It would pave it".

"It would increase the risks of nuclear proliferation and the risks of a horrific war," he added.

Israel is the Middle East's sole, albeit unacknowledged, nuclear power.

Repeating previous Israeli warnings, Intelligence Minister Yuval Steinitz said Thursday that all options were open.

"If we have no choice, we have no choice... the military option is on the table," he said.

Israel has been the loudest opponent of reaching a deal that would leave Iran with atomic capabilities.

Shortly after the outline of the deal was revealed, Israeli government officials slammed it as "a historic mistake which will make the world far more dangerous".

"It is a bad framework which will lead to a bad and dangerous agreement," they said on condition of anonymity.

But analysts said it was tough diplomacy -- not military strikes -- that would be the focus of Israeli efforts after Thursday's announcement, at least in the short term.

"After the entire world signed an agreement with Iran, I don't see Israel striking Iran nuclear facilities tomorrow morning," said Yoel Guzansky, the former head of the Iran desk at Israel's National Security Council.

"It will be seen as jeopardising global security," he said.

"However if the Iranians were caught cheating, then it's a different ball game, then you have the legitimacy to do other things."

Under the framework, nuclear-related US and EU sanctions against Iran will be lifted once the UN atomic watchdog has verified that Tehran has implemented its promises.

Yossi Kuperwasser, until recently the director general of Israel's strategic affairs ministry, said Netanyahu would be seeking to keep up pressure right up until a final accord, which is due to be drafted by the end of June.

Netanyahu should "keep the military option on the table. Not only the military option -- keep doing whatever is necessary to prevent Iran from having the nuclear capability," Kuperwasser said.

- 'Iranians will be careful' -

Discussion of an Israeli military attack on Iran's nuclear facilities peaked in 2011-2012, when Ehud Barak was defence minister and Netanyahu premier.

But Kuperwasser said talk of an attack does not necessarily translate into action.

"As long as you have a credible military option, the Iranians will be very careful to not put you in a position where you will have to use it," he said.

Emily Landau, an expert on nuclear strategy and arms control at the Institute for National Security Studies in Tel Aviv, said Israel is limited in what it can do in the face of what it considers to be a bad deal.

"It breaks down to attempts to convince" the world powers negotiating with Iran to reach a better agreement, she said.

"This is what it's been doing the whole time, and will continue doing with greater vigour," she said.

She said that Netanyahu's recent statements have been less focused on military options.

"There is definitely a change in the nuance, the rhetoric has changed," she said.

"We no longer hear these insinuated threats of a military attack (on Iran's nuclear facilities) from Netanyahu," Landau said.

Some analysts warned Israel needs to stop looking at the Iranian issue in isolation.

Yehezkel Dror, a political science professor at the Hebrew University, said Israel was making "a severe mistake" in considering the conflict with the Palestinians and the Iranian issue as separate.

"If there will not be progress toward a peace accord that would look reasonable to the US and others -- and which would enable more cooperation with other anti-Iranian Arab states in the region -- our standings won't improve," he said.

The last round of Israeli-Palestinian peace talks broke down last year amid mutual recriminations, despite a strong push from Washington.

"Progress toward a peace agreement," even if it doesn't reach the final goal of an accord, "will also enable Israel to act, if the need arises, against Iran," Dror said.

US Republicans skeptical, hostile to Iran nuclear deal
Washington (AFP) April 3, 2015 - US Republicans expressed skepticism about Thursday's deal to curb Iran's nuclear program, with House Speaker John Boehner demanding Congress be allowed to review the accord before crippling economic sanctions are lifted.

Several House and Senate members expressed cautious optimism about what President Barack Obama called a "historic understanding" reached between six world powers and Iran, a deal he assured would, if followed, prevent Iran from developing a nuclear bomb.

Boehner slammed it as an "alarming departure" from the White House's initial goals, suggesting the Obama administration caved to Iranian negotiators and allowed certain concessions.

"My immediate concern is the administration signalling it will provide near-term sanctions relief," Boehner said in a statement.

"Congress must be allowed to fully review the details of any agreement before any sanctions are lifted."

According to parameters released by the White House, sanctions on Iran will be suspended "after the IAEA (International Atomic Energy Agency) has verified that Iran has taken all of its key nuclear-related steps," but they could snap back into place if Iran fails to fulfill its commitments.

Senator Mark Kirk, among the most hawkish Republicans on Iran and co-author of legislation that tightens sanctions, minced no words in reacting to the agreement.

"Neville Chamberlain got a better deal from Adolf Hitler," Kirk sneered, referring to the 1930s British prime minister and his disastrous policy of Nazi appeasement.

Obama starkly warned lawmakers that if Congress "kills this deal... then it's the United States that will be blamed for the failure of diplomacy."

Republican 2016 presidential hopefuls challenged the accord's viability.

Former Florida governor Jeb Bush described the agreement as "flawed", arguing it included "significant concessions to a nation whose leaders call for death to America and the destruction of Israel."

"Nothing in the deal described by the administration ... would justify lifting US and international sanctions," Bush said.

Former Texas governor Rick Perry said on Twitter that Americans have a right to be wary of a deal "riddled with concessions by the Obama administration," while Senator Marco Rubio warned that Iran being able to keep 6,000 of its 19,000 centrifuges indicates "that this deal is a colossal mistake."

Senate Foreign Relations Committee chairman Bob Corker urged lawmakers to "remain clear-eyed" about Iran, and reiterated his insistence that Congress review any final deal with the Islamic republic.

Corker introduced legislation that would compel Obama to run the accord past Congress.

He said there was "growing bipartisan support for congressional review of the nuclear deal," adding he was "confident of a strong vote on the Iran Nuclear Agreement Review Act" when his committee takes it up on April 14.

Senate Democrat Robert Menendez also backed congressional action.

"If diplomats can negotiate for two years on this issue, then certainly Congress is entitled to a review period of an agreement that will fundamentally alter our relationship with Iran and the sanctions imposed by Congress," he said.

Senate Minority Leader Harry Reid said he was cautiously optimistic about the deal, and warned against "rash action" in Congress.

"In the coming days and weeks, we should all take a deep breath, examine the details and give this critically important process time to play out," he said.