“I may not know about all of their capabilities but I think that it’s a fair characterization to say that they could delay but not destroy Iran’s nuclear capabilities,” he said.

U.S. officials have stressed that Washington could deal a decisive blow to Iran’s nuclear sites, if necessary, and will not allow Tehran to obtain a nuclear weapon. It’s unclear whether those assurances will be enough to forestall Israeli action.

For Israel to carry out a long-threatened strike on Iranian nuclear sites, it would have to overcome dissent within its governing coalition that reflects public fear of igniting an unprecedented missile war.

Prime Minister Benjamin Netanyahu says that scenario would be “dwarfed” by the prospect of an Iranian bomb, which he describes as tantamount to a second Holocaust - language that seems to herald a Jewish call to arms.

But the popular, conservative leader has not proven very persuasive. While surveys show a growing minority - now 32 to 35 percent - of Israelis favor taking Iran on alone, more are opposed. Around a quarter are undecided.

(Additional reporting by Dan Williams in Jerusalem; Editing by Eric Beech)