Postpublished at 16:51 Greenwich Mean Time 3 March 2015
But Mr Netanyahu says he knows the US will stand with Israel.
Mr Netanyahu addressed the US Congress about the threat posed by Iran's nuclear programme
The Israeli leader said: "Iran has proven time and again that it cannot be trusted"
Congressmen and women rose to their feet several times to give him warm ovations
The invitation, made by House Speaker John Boehner, is seen as a rebuke to Mr Obama's threat to veto new sanctions on Iran
The US, Britain, France, Germany, Russia and China are currently working on an interim agreement with Iran for the end of March
All times in GMT
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But Mr Netanyahu says he knows the US will stand with Israel.
By Jeremy Bowen's count, Mr Netanyahu has received 19 standing ovations so far.
Mr Netanyahu says after thousands of years, the Jewish people can defend themselves. "Even if Israel has to stand alone, Israel will stand."
Jeremy Bowen
BBC Middle East editor
tweets, external: "This is a direct intervention in US politics. He wants Congress to vote down a deal if it gets the chance."
Ian Black, Guardian's Middle East editor
Iran has 'voracious appetite for aggression' and is 'gobbling up four countries' are both wild exaggerations in #NetanyahuSpeech
Peter Beaumont, Jerusalem correspondent, Guardian and Observer
tweets:, external #Bibispeech really not munch new in Bibi's speech. he has been saying this for yonks. No new beef. No new detail. Same hyperbole
Standing up to Iran and other regimes is not easy, Mr Netanyahu says, motioning towards Ellie Wiesel in the gallery.
Benjamin Netanyahu speaks at the podium in Congress
Paul Adams, BBC News
tweets, external: "Not every member of Congress rises to applaud when Bibi says it's a bad deal and we're better off without it. But most do."
Mr Netanyahu says the alternative to this deal is not war but a "much better deal".
Mr Netanyahu has received a warm reception in Congress.
"If Iran wishes to be treated like a normal country, let it act like a normal country," Mr Netanyahu says.
"This deal won't change Iran for the better, it will only change Iran for the worse" - and would lead to a nuclear arms race in the Middle East, Mr Netanyahu said.
Such a deal would "pave the way" for a Iran nuclear deal - and would make the country more aggressive.
Mr Netanyahu argues Iran could eventually be "weeks away" from a full nuclear arsenal, when deal expires.
Mr Netanyahu is speaking to a full Congress.
Jeremy Bowen
BBC Middle East editor
tweet, external: #NetanyahuSpeech crucial point for his thesis. Iran can't be trusted in any circumstances. and restrictions will expire in a decade.
Mr Netanyahu says Iran both "defies" nuclear inspectors and plays "hide and cheat" with them.
Mr Netanyahu says the current negotiations would leave Iran's nuclear programme "largely intact".