Israeli Prime Minister Benjamin Netanyahu, who's arrived in Washington ahead of a controversial speech to Congress, claims the trip is a "fateful mission, and even historic".
Netanyahu arrived on Sunday evening at his downtown Washington hotel just one block from the White House under police escort.
He passed through a white marquis set up at the back entrance of the hotel while black-cloaked security agents kept watch from the building's perches.
Netanyahu hopes his speech on Tuesday will convince politicians and the American public that an initial framework agreement being negotiated between Iran and Western powers is "dangerous".
The prime minister was invited to speak to Congress by Republicans who didn't consult the White House, which angered President Barack Obama.
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Critics have slammed the speech as an intervention into US politics and inappropriate given that Netanyahu is in the midst of a re-election campaign. Parliamentary polls are set for March 17.
Netanyahu's aides insist the speech can't be put off because of the timetable of the Iranian nuclear negotiations.
"I feel a representative of all Israeli citizens, also those who don't agree with me," Netanyahu said before boarding his plane.
"I feel a deep and honest concern about the security of all the citizens of Israel, the fate of the state and the fate of our people. I will do all in my power to safeguard our future," he said.
Obama will not meet Netanyahu during his stay in Washington.
Netanyahu said Saturday in Jerusalem during a visit to the Wailing Wall he respected Obama and believed in the strength of US-Israeli relations.
Republicans who control both chambers of Congress are seeking greater sanctions against Iran, but Obama has called on them to hold off while negotiations continue.
Iran is negotiating a deal with Britain, China, France, Russia, the US and Germany to curb Tehran's uranium enrichment and other parts of its nuclear program in return for ending economic sanctions on Tehran.
They hope to reach a framework agreement by the end of March and a final deal by mid-year that would end longstanding concerns over Iran's nuclear program and its military capabilities.
