Prime Minister Benjamin Netanyahu again warned Monday that Washington's bid to sign a nuclear accord with Iran could threaten Israel's very survival, but insisted ties remain strong.

The Israeli leader's lobbying trip to Washington came as US Secretary of State John Kerry was in Geneva for talks with his Iranian counterpart on what would be an historic deal.

Netanyahu's visit -- including an address the US Congress on Tuesday -- is seen as a last ditch bid to derail that effort, a key goal of President Barack Obama's foreign policy.

But he denied that his action had harmed the traditionally close US-Israeli alliance.

"You are here to tell the world that reports of the demise of the US relationship is not only premature, but it is wrong," Netanyahu told a packed pro-Israel conference in Washington.

Netanyahu will go to Capitol Hill on Tuesday to address a joint meeting of Congress on the perils of Obama's efforts to reach agreement with Iran to curtail its nuclear program.

He was invited by Speaker of the House John Boehner, a Republican, and he accepted with neither party informing the White House.

"My speech is not intended to show any disrespect to President Obama or the office that he holds. I have great respect for both," he told thousands of activists at the lobby group AIPAC's annual conference.

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

"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 senior diplomats from Iran and the United States began a new round of talks Monday in Switzerland.

Kerry and Iranian Foreign Minister Mohammad Javad Zarif met in a lakeside hotel in Montreux for a series of sessions which are scheduled to stretch into Wednesday afternoon.

The pace of the negotiations to hammer out a deal to rein in Iran's suspected nuclear arms program in exchange for sanctions relief has gathered pace as a March 31 deadline nears.

Speaking before Netanyahu, Washington's ambassador to the United's address Nations Samantha Power sought to counter his opposition to the emerging deal with Tehran.

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

And she insisted that Obama would stand by US allies "whether the negotiations collapse or produce a diplomatic solution that meets our bottom line."

Netanyahu aides say Israel has "excellent information" that talks between the Islamic republic and the so-called P5+1 group negotiating the deal are heading toward an easing of international sanctions without the ironclad safeguards the Jewish state says are essential to deny Iran a nuclear bomb.

"We know a great deal about the emerging agreement," an official told journalists on Netanyahu's flight to Washington Sunday. "In our view, it is a bad agreement."

- Thunderous applause -

The official, who spoke on condition of anonymity, would not indicate the source of the information but said Netanyahu would elaborate in his congressional address.

State Department spokeswoman Marie Harf said Monday that if the details came from confidential US briefings to Israeli officials, revealing them would be a betrayal.

"We've continuously provided detailed classified briefings to Israeli officials to keep them updated and to provide context," she said.

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

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

Netanyahu's opponents at home and abroad accuse him of endangering the special relationship with the United States in order to further his policy agenda.

He is running for reelection in a March 17 general election.

Similar criticism has been levelled at Obama's Republican opponents in the US Congress.

"Our commitments to our partnership with Israel are bedrock commitments rooted in shared fundamental values cemented through decades of bipartisan reinforcement," Power said.

"This partnership should never be politicized," she added, vowing that the joint commitments "cannot and will not be tarnished or broken."

Washington political journal The Hill said that 42 Democrat lawmakers plan to boycott Netanyahu's speech on Tuesday.

At Monday's conference, Netanyahu won thunderous applause and a standing ovation.

House Foreign Affairs Committee chairman Ed Royce, who was in the audience, said Netanyahu struck the right tone.

"The issue here is about Iran, about Iran getting undetectable nuclear breakout capability," he told AFP.

"We've been gradually lifting sanctions, releasing the pressure on Iran while Iran continues to move forward."