US President Barack Obama said there was "nothing new" in Benjamin Netanyahu's controversial speech to Congress Tuesday, insisting the Israeli Prime Minister did not offer a better option than negotiations.

Netanyahu "did not offer any viable alternatives," Obama said speaking from the Oval Office.

Netanyahu earlier, before an impassioned joint meeting of Congress, pilloried talks with Iran, which if successful would be a key plank of Obama's foreign policy legacy.

Receiving a warm welcome from Obama's Republican foes, Netanyahu insisted the deal "doesn't block Iran's path to the bomb. It paves Iran's path to the bomb."

Obama has refused to meet Netanyahu during his visit to the US capital and said he did not watch the speech but saw a transcript.

"I am not focused in the politics of this, I am not focused on the theatre," Obama said.

"As far as I can tell, there was nothing new."

"On the core issue, which is how to prevent Iran from obtaining a nuclear weapon which would make it far more dangerous, the prime minister did not offer any viable alternatives."

"We don't yet have a deal," he added. "But if we are successful, then in fact this will be the best deal possible with to prevent Iran from obtaining nuclear weapon."

As Obama was speaking, talks between the United States and Iran to reach an agreement continued in Switzerland.

The deal would limit Iranian nuclear activity for a decade or more, but would not completely dismantle facilities that could be used to make a bomb.

Iran says it does not want a nuclear weapon.