Israeli Prime Minister Benjamin Netanyahu was to address the U.S. Congress Tuesday in an increasingly heated battle with the White House over Tehran's nuclear ambitions, as tough talks resumed in Switzerland.

Netanyahu has repeatedly attacked the emerging Iran deal and is reportedly planning to unveil classified details shared by the U.S. to lawmakers to show why he believes it poses a grave danger to Israel.

But US President Barack Obama lashed out at Netanyahu, pointing to the premier's past assaults on an interim deal reached in 2013 under which Iran has already halted much of its uranium enrichment program.

"Netanyahu made all sorts of claims," he told Reuters on Monday.

"This was going to be a terrible deal," he went on. "This was going to result in Iran getting $50 billion worth of relief. Iran would not abide by the agreement. None of that has come true."

Netanyahu will be speaking as U.S. and Iranian negotiators are hammering out the deal behind closed doors in a lakeside hotel in Montreux, with a March 31 deadline looming.

Thousands of miles from the political storm unfolding in Washington, top U.S. diplomat John Kerry and his Iranian counterpart Mohammad Javad Zarif met for two hours after two brief sessions on Monday.

Talks were due to resume later Tuesday, with discussions due to stretch into Wednesday.

A senior State Department official told AFP Kerry would not be watching Netanyahu's speech live as he would be in talks, but would be briefed later about the content.

Zarif however reacting to Obama's comments that any deal should stay in place for a "double-digit" period of years, warned his country "will not yield in the face of excessive demands and the illogical posture of the other party."

"It is clear that Mr Obama's posture is aimed at winning public support and countering the propaganda of the prime minister ... using unacceptable and threatening terms and formulations."

State Department spokeswoman Marie Harf meanwhile warned Netanyahu against revealing details of the deal shared in confidence with the Israelis.

"Any release of any kind of information like that would, of course, betray that trust," she said Monday.

"We want to keep talking in these settings, of course, but that would be a problem."

Netanyahu believes the so-called P5+1 group of global powers is planning to ease international sanctions without the ironclad safeguards needed to deny Tehran a nuclear bomb.

The U.S. administration says that is not true, and warned that Netanyahu could unravel the negotiations if he mobilizes U.S. lawmakers in the Republican-held Congress against it.

Israel itself is understood to have nuclear weapons but has never officially admitted to having such an arsenal.

- No nuclear arms for Iran -

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Samantha Power, the U.S. ambassador to the United Nations, weighed into the fight on Monday when she addressed 16,000 pro-Israel activists in the US capital.

"The United States of America will not allow Iran to obtain a nuclear weapon, period," she said.

Taking the podium shortly after Power, Netanyahu remained unswerving in his opposition to Obama's policy.

"The purpose of my address to Congress... is to speak up about a potential deal with Iran that could threaten the survival of Israel," he said.

"My speech is not intended to show any disrespect to President Obama," he told the lobby group AIPAC's annual conference.

"Israel and the United States agree that Iran shouldn't have nuclear weapons. But we disagree on the best way to prevent them from developing those weapons."

The Obama administration is furious that Netanyahu was invited to address Congress by Republican Speaker John Boehner, without either party informing the White House.

The speech is also being viewed in the U.S. as part of Netanyahu's campaign for a third consecutive term with Israeli elections due on March 17.

It's clear the Iran talks have reached a critical stage, and German Foreign Minister Frank-Walter Steinmeier said in Geneva that in a decade of negotiations "it's the first time that I have the impression that the Iranians want to negotiate seriously.

Asked about Israel's security, Steinmeier replied: "There won't be a bad deal, there'll only be a deal which will prevent Iran from gaining access to a nuclear weapon." (AFP)