Israeli prime minister Benjamin Netanyahu has insisted that his plans to address Congress are not aimed at disrespecting President Barack Obama, even as he assailed the US leader's bid for a nuclear deal with Iran as a threat to his country's survival.
"I have a moral obligation to speak up in the face of these dangers while there is still time to avert them," Mr Netanyahu said during an address to a pro-Israel lobbying group in Washington.
As Mr Netanyahu spoke, secretary of state John Kerry was opening a new round of talks with Iran in Geneva aimed at reaching a framework nuclear deal ahead of a late March deadline.
Mr Netanyahu's visit to Washington has exposed deep tensions with the White House. The centrepiece of his trip is an address to Congress tomorrow which was arranged by Republicans without the knowledge of the Obama administration.
In a preview of his speech to politicians, Mr Netanyahu suggested that Mr Obama did not understand the depth of Israeli concerns about Iran's pursuit of a nuclear bomb.
"US leaders worry about the security of their country," he said. "Israeli leaders worry about the survival of their country."
Despite his sharp rhetoric, Mr Netanyahu declared that the relationship between the US and Israel remains strong.
"Reports of the demise of the Israeli-US relationship is not only premature, they're just wrong," Mr Netanyahu said. "Our alliance is stronger than ever."
Mr Netanyahu's remarks at the annual policy conference of the American Israel Public Affairs Committee were being bracketed by speeches from a pair of senior US officials: UN ambassador Samantha Power and national security adviser Susan Rice.
Ms Power spoke warmly of the ties between the long-time allies, saying the relationship "should never be politicised". She defended Mr Obama's pursuit of an accord with Iran and said the president shared Israel's commitment to preventing Tehran from obtaining a nuclear weapon.
"If diplomacy should fail, we know the stakes of a nuclear-armed Iran," she said. "We will not let it happen."
Ms Rice was expected to deliver a more specific rebuttal to Mr Netanyahu's criticism of the US-led nuclear negotiations. She has also been among the most outspoken critics of the prime minister's plan to address Congress, calling the move "destructive" to the US-Israel relationship.
Mr Netanyahu has long been suspicious of Mr Obama's negotiations with Iran, fearing the US and its negotiating partners are prepared to leave Tehran on the cusp of developing a nuclear weapon. He has stepped up his public criticism as the parties inch closer to the March deadline.
US and Israeli officials have reported progress on a deal that would freeze Iran's nuclear programme for 10 years but allow it to slowly ramp up in the later years of an agreement. Mr Netanyahu has vigorously criticised the contours of such an agreement, saying it suggests the US and its partners have "given up" on stopping Iran from being able to get a bomb.
A Netanyahu adviser told reporters travelling with the prime minister to Washington that Israel was well aware of the details of the emerging nuclear deal and that they included Western compromises that were dangerous for Israel. Still, he tried to lower tensions by saying that Israel "does not oppose every deal" and was merely doing its best to warn the US of the risks.
Mr Kerry, who is in Switzerland for the next round of nuclear negotiations, warned Israel against releasing "selective details" of the negotiations.
"Doing so would make it more difficult to reach the goal that Israel and others say they share," Mr Kerry said.
The US is negotiating alongside Britain, France, Germany, Russia and China.