The US and Israeli air war against Iran began with attacks against Tehran on Saturday, killing Iranian Supreme Leader Ali Khamenei, and prompting Iranian retaliation against Israel and missile attacks at Arab nations with US bases across the Middle East.
President Donald Trump initially projected the war to last four to five weeks, but added it could go on longer, and has since sought to justify a broad, open-ended war on Iran.
Netanyahu rejected the idea of the conflict lasting years, like previous wars in the region.
"I said it could be quick and decisive. It may take some time, but it's not going to take years. It's not an endless war," Netanyahu said on Fox News' Hannity program on Monday.
He said it was crucial to "act now" against Iran because the leadership in Tehran was building underground facilities to shield its missile and nuclear programs from attacks.
"We had to act now.
"If no action was taken now, no action could be taken in the future," Netanyahu said.
"They started building new sites ... underground bunkers that would make their ballistic missile program and their atomic bomb program immune within months," Netanyahu said.
Iran posed "existential threats ... to the entire world", he said on X.
The assault on Iran formed part of a list of Trump's foreign policy actions that have marked a striking shift from his "America First" rhetoric against US interventions when he campaigned in the 2024 elections.
Netanyahu said he saw the war as an opportunity for lasting peace in the Middle East, including between Israel and Saudi Arabia.
"Yes I do," he said, when asked if he saw a lasting path to peace in the region.
A Reuters/Ipsos poll showed over the weekend that only one-in-four Americans approved of USstrikes on Iran that have plunged the Middle East into chaos.
US wars in Iraq and Afghanistan that lasted several years made many Americans sceptical of Washington's direct involvement in wars on foreign soil.
Netanyahu said the US and Israel's war against Iran was creating a scenario for the Iranian people to topple their government.
"Now, of course, it's up to the people of Iran in the final count to change the government, but we are creating - America and Israel together are creating - the conditions for them to do so," he said.
with dpa
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