US President Barack Obama on Monday sought to assure Prime Minister Binyamin Netanyahu that the United States would always "have Israel's back," but said there was still time for diplomacy.

Netanyahu, in a show of unity with an American leader with whom he has had a rocky relationship, said at the White House that both Israel and the United States stood together on the need to prevent Iran from obtaining nuclear weapons.

"The bond between our two countries is unbreakable," Obama said. "The United States will always have Israel's back when it comes to Israel's security."

Sitting side by side and smiling at each other in the Oval Office, the two leaders sought to present a united front in the Iranian nuclear standoff after weeks of mounting concern that Israel would preemptively strike Iran on its own.

In one of the most consequential meetings of US and Israeli leaders in years, they made no mention of any differences they may have over red lines that could trigger military action to curb an Iranian nuclear program that Israel sees as a threat to its existence.

"We believe there is still a window that allows for a diplomatic resolution," Obama said.

Netanyahu made clear that Israel would be the "master of its fate" in deciding how to deal with Iran, which has called for the destruction of the Jewish state.

"It must have the ability to defend itself, by itself, against any threat," Netanyahu said, echoing remarks Obama made a day earlier in a speech to the American Israel Public Affairs Committee Policy Conference on Sunday.

Obama has been urging Israel to allow sanctions more time to work against Iran's nuclear ambitions while balancing that with assurances of his resolve to do whatever is necessary to keep the Islamic republic from becoming a nuclear-armed state.

At the White House meeting, Obama told Netanyahu the United States reserved "all options" in dealing with Iran. The president has made clear that would include a possible military component.

"We do not want to see a nuclear arms race in the most volatile region in the world," Obama said.

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