Netanyahu, who faces an intensifying corruption probe at home, was among friends in the US capital, where he delivered a speech to the influential American Israel Public Affairs Committee (AIPAC) a day after talks with President Donald Trump.
He thanked Trump for his vow to tear up the 2015 Iran nuclear deal if it is not strengthened to prevent Tehran from resuming its alleged quest for atomic weapons, and said Israel and its Arab neighbors would back such a move.
"Darkness is descending on our region. Iran is building an aggressive empire," he declared, accusing Tehran of exploiting its role supporting Bashar al-Assad in Syria's civil war to set up permanent bases on Israel's border.
"The force behind so much of what is bad is this radical tyranny in Iran. I have a message for you today, it's a very simple one: we must stop Iran, we will stop Iran," he said.
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Iran insists it never intended to build a nuclear weapon, but has warned it could rapidly restore its capacity if the United States breaches the deal by restoring crippling economic sanctions.
Israel and Trump see the deal's time limits as tantamount to providing Tehran with a path to the bomb, and argue that Iran has not moderated its behavior, but instead is playing an ever more dangerous game in its region.
Netanyahu used his AIPAC speech to argue that Washington and Israel would not be alone when they choose to confront Iran, saying many Arab countries would side with the Jewish state over their common enemy.
"That is true for Egypt and Jordan, Israel's long time peace partners, but it is also true for many other Arab countries in the Middle East.