US President Barack Obama says Mr Netanyahu has not "offered any viable alternatives" to negotiating with Tehran. Photo: BBC

In a speech to the US Congress, Benjamin Netanyahu warned that a deal under discussion on Iran's nuclear programme could "pave Iran's path to the bomb" rather than block it.

But Mr Obama said Mr Netanyahu had offered no viable alternative.

Other senior Democrats - and Iran - also criticised Mr Netanyahu.

The Israeli leader's visit was controversial from the start, because the Republican speaker invited him without consulting the White House.

The US president announced he would not meet Mr Netanyahu, who is fighting in a closely contested national election in just two weeks' time.

Talks on Iran's nuclear programme are nearing a critical late-March deadline for an outline agreement to be reached.

'Hide and cheat'

In a speech to the US Congress regularly punctuated by standing ovations Mr Netanyahu depicted Iran as a "threat to the entire world".

Mr Netanyahu was searing in his denunciation of the deal being negotiated with Iran

His speech was interrupted by regular standing ovations from US lawmakers

But some, such as House Democratic Leader Nancy Pelosi (right), held back applause and sometimes showed visible signs of disagreement

Mr Netanyahu's speech, with handwritten edits, urged US lawmakers to block any forthcoming deal with Iran

He insisted Iran had proven time and time again that it could not be trusted.

Mr Netanyahu went on to criticise the likely contours of the deal currently being negotiated in Switzerland, where Iranian Foreign Minister Javad Zarif met US Secretary of State John Kerry on Tuesday.

"We've been told that no deal is better than a bad deal," he said. "Well this is a bad deal, a very bad deal, We're better off without it."

He said it relied heavily on international monitoring, when Iran "plays a pretty good game of 'hide and cheat' with UN inspectors".

Analysis: BBC Middle East editor Jeremy Bowen

The speech was classic Netanyahu. He mixed the politics of fear with the politics of bravery in adversity. Iran was gobbling up Middle East states - a reference to its influence in Syria, Lebanon, Iraq and Yemen - while Israel stood strong, never again allowing the Jews to be passive victims.

It was a direct intervention in American politics. Prime Minister Netanyahu wants the Congress to do all it can to block an agreement with Iran, if one is made.

Iran, he said, must change its aggressive behaviour before any deal.

Mr Netanyahu's critics say he's manipulating the close relationship between Israel and the US for political advantage. Democratic leader Nancy Pelosi said she was close to tears during the speech - because it was condescending and insulted the intelligence of Americans.

But there's no doubt that Mr Netanyahu sees the threat from Iran as real, and his skilful rhetoric will connect with many Americans. If there is a deal, President Obama will need to deploy his own considerable way with words to sell it to his own people.

Key quotes: Netanyahu speech

Jon Sopel: 'Chutzpah' riles Obama

Mr Netanyahu received a rapturous reception for his speech, but dozens of Democrats - including Vice President Joe Biden - stayed away.

House minority leader Nancy Pelosi at times refused to clap and laterissued a statement saying Mr Netanyahu's speech had been an "insult to the intelligence of the United States" that had left her near tears.

'Boring and repetitive'

Mr Obama said he had been unable to watch the speech as it was given, but found "nothing new" when he read the transcript.

"The alternative that the prime minister offers is 'no deal', in which case Iran will immediately begin once again pursuing its nuclear programme, accelerate its nuclear programme without us having any insight into what they are doing and without constraint," he said.

He said sanctions alone were not sufficient without offering Iran an alternative path.

The state department later complained about Mr Netanyahu's claim that Mr Kerry had "confirmed last week that Iran might legitimately possess" 190,000 centrifuges enriching uranium by the end of any deal and would be "weeks away" from an "arsenal of nuclear weapons".

The state department said: "That's not what Kerry said. He [said]: 'If you have a civilian power plant that's producing power legitimately and not a threat to proliferation, you could have as many as 190,000."

Other Democrats criticised the speech, with Representative John Yarmuth calling it "straight out of the Dick Cheney playbook - fear-mongering at its worst".

Meanwhile, Iran's foreign ministry said Mr Netanyahu's words were "boring and repetitive", Fars news agency reported.

Iranian Foreign Ministry Spokeswoman Marzieh Afkham said the "Iranophobic" speech was a "deceitful show and part of the election campaign of Tel Aviv's hardliners".

Analysis: Kevin Connolly, BBC News, Jerusalem

Mr Netanyahu's speech also played to an Israeli audience - two weeks before he fights for re-election

Benjamin Netanyahu's rivals in Israel's election face a dilemma as the applause from the speech in Washington begins to die down.

It's been hugely frustrating for them to watch him walking the world stage and worse still watching the speech on television.

They are the kind of television images you cannot buy in an election campaign - the Houses of Congress rising repeatedly in standing ovations.

But if they repeat their warnings that Mr Netanyahu is endangering Israeli security by alienating the White House they risk protracting a story which has played to the prime minister's advantage.

Many of them, like the opposition leader Yitzhak Herzog, feel they're just as tough on Iran as Mr Netanyahu - they just don't have access to the world stage as he does.

The US, UK, France, Germany, Russia and China are seeking to reach agreement to curtail Iran's nuclear programme in exchange for sanctions relief.

They fear Iran has ambitions to build a nuclear bomb - something Iran denies, insisting it is merely exercising its right to peaceful nuclear power.

Negotiators are currently working towards a late-March deadline for an outline agreement with Iran, which would be followed by a detailed deal by the end of June.

Nuclear Iran: What world powers want - and what they fear

• World powers imposed sanctions on Iran because they felt it was not being honest about its nuclear programme and was seeking the ability to build a nuclear bomb.
• Tehran denied this. Talks between Iran and six world powers known as the P5+1 have tried to allay the suspicions in exchange for easing the sanctions
• Specifically, the world powers want to curtail Iran's ability to enrich uranium, which can be used to make reactor fuel but also nuclear weapons
• Disagreement centres on how to limit Iran's development and use of centrifuges that enrich uranium
• Faster enrichment would cut the time Iran would need to produce enough weapons-grade uranium for a weapon, were it to choose to do so. The US wants this "break-out window" to be at least a year long
• It is not known if Iran has a warhead or suitable delivery system