Israeli Prime Minister Benjamin Netanyahu has told US President Barack Obama that Israel must always remain "master of its fate"
Meeting the Israeli leader at the White House, Mr Obama said a nuclear Iran would be an "unacceptable" development.
On Sunday, Mr Obama told a pro-Israel conference in Washington there had been too much "loose talk" of war with Iran.
Israel fears Iran is seeking to develop nuclear weapons, although Tehran insists its nuclear plans are peaceful.
"The bond between our two countries is unbreakable," Mr Obama said, as the two leaders sat side-by-side in the Oval Office.
The president emphasised: "We believe there is still a window that allows for a diplomatic resolution," but added that the US would consider "all options" in dealing with Iran.
Meanwhile, Mr Netanyahu said Israel "must have the ability to defend itself, by itself, against any threat".
After years of international pressure and the repeated failure of negotiations and offers of talks with Tehran, talk has grown in recent months of a pre-emptive strike against Iranian nuclear facilities.
The US has pushed for the imposition of ever-stricter sanctions against Iran, including recent curbs on its central bank and its ability to export oil to the West.
Yet despite the ratcheting up of sanctions, speculation has been mounting that Israel might choose to attack Iran sometime during 2012.
Hours before the two leaders held bilateral meetings the head of the UN nuclear agency, Yukiya Amano, reiterated that the organisation had "serious concerns" that Iran could be hiding secret work on developing atomic weapons.
Reiterating concerns detailed in an agency report, he said the organisation was unable "to conclude that all nuclear material in Iran is in peaceful activities".
Mr Obama and Mr Netanyahu - who have disagreed on Middle East policy in the past - were due to spend the morning in meetings at the White House.
A first session, in the Oval Office, would be an opportunity to discuss "a range of strategic issues of mutual concern", the White House said.
Next, the two leaders are scheduled to meet for a private working lunch at the White House.
At the end of the day Mr Obama is scheduled to meet US Defence Secretary Leon Panetta.
Mr Obama and Mr Netanyahu are said to have a famously cool relationship. In May 2011, during a visit to Washington, correspondents widely noted the frosty body language between the two leaders.
In November 2011, at a G20 summit, journalists overheard a private exchange between French President Nicolas Sarkozy and Mr Obama in which Mr Sarkozy called the Israeli leader a "liar".
Mr Obama replied: "You may be sick of him, but me, I have to deal with him every day."
In his speech on Sunday to the American-Israel Public Affairs Committee (Aipac), Mr Obama said the US "will not hesitate" to use force to stop Iran obtaining nuclear weapons.
But he stressed that diplomacy could still succeed.
"Iran's leaders should know that I do not have a policy of containment - I have a policy to prevent Iran from obtaining a nuclear weapon," Mr Obama told the annual Aipac conference.
"And as I've made clear time and again during the course of my presidency, I will not hesitate to use force when it is necessary to defend the United States and its interests."
However, he said Iran was isolated and there was an opportunity "for diplomacy - backed by pressure - to succeed".
"Already, there is too much loose talk of war," Mr Obama added.
"Over the last few weeks such talk has only benefited the Iranian government, by driving up the price of oil which they depend upon to fund their nuclear programme."
Mr Netanyahu is due to make a keynote address to the Aipac conference on Monday night.----
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In: World News, Politics, Iran
Tags: Israel, US, Iran, strike, nuclear, tensions, politics
Location: Washington, District of Columbia, United States (load item map)
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