JERUSALEM (AFP) - United States Ambassador Dan Shapiro on Monday sought to quell Israeli fears over an emerging deal with Iran, vowing that Washington would never let Teheran acquire a nuclear weapon.

"On this crucial issue, the US and Israel share an identical agenda," Mr Shapiro told delegates attending the General Assembly of the Jewish Federations of North America in Jerusalem.

US President Barack Obama "has made it crystal clear that he will not permit Iran to acquire a nuclear weapon period, and is prepared to use all elements of our national power to ensure that we are successful", he said.

His remarks were made as the US and Israel were locked in an escalating war of words over negotiations between world powers and Iran in a bid to halt its nuclear programme, which is widely believed to be a front for developing a military capability.

Diplomats have said they are closing in on an interim agreement that will freeze or curb some of Iran's nuclear activities in exchange for an easing of the tight sanctions on the Islamic republic, after failing to secure a deal at weekend crunch talks in Geneva.

In recent days, Israel's Prime Minister Benjamin Netanyahu has furiously denounced the emerging agreement as "dangerous", reaching out to world leaders and to the American public to get his point across.

"Iran gives practically nothing and it gets a hell of a lot. That's not a good deal," Mr Netanyahu told CBS on Sunday.

"It's a bad and dangerous deal that deals with the thing that affects our survival," he told participants of the JFNA's assembly. "And when it comes to the question of Jewish survival and the survival of the Jewish state, I will not be silenced."

However, US Secretary of State John Kerry, who took part in the Geneva talks, rejected Mr Netanyahu's remarks, insisting Washington was neither "blind" nor "stupid" when it comes to Iran's nuclear ambitions.