Hillary Clinton, in her most bellicose comments since the presidential race began 15 months ago, yesterday threatened to "totally obliterate" Iran if it launched a nuclear strike against Israel.

Speaking as voters went to the polls in the Pennsylvania primary, she said: "I want the Iranians to know that if I'm the president, we will attack Iran" if it attacks Israel.

Barack Obama accused her of sabre-rattling, saying this was the kind of language that had been used by the Bush administration over the last few years and was not helpful.

In an interview with ABC's Good Morning America, Clinton was asked what she would do if Iran attacked Israel with nuclear weapons.

She replied: "In the next 10 years, during which they might foolishly consider launching an attack on Israel, we would be able to totally obliterate them. That's a terrible thing to say but those people who run Iran need to understand that, because that perhaps will deter them from doing something that would be reckless, foolish and tragic."

US policy, whether Republican or Democrat, is to retaliate with nuclear weapons against anyone launching a nuclear strike against Israel.

In spite of Clinton's harsh words yesterday, both she and Obama have said on the campaign trail they would like to begin fresh negotiations with Tehran over its suspected nuclear weapons programme. Obama has gone further by saying he would like to speak face to face with the Iranian leader, Mahmoud Ahmadinejad, while Clinton has suggested a more cautious approach, with strict conditions agreed beforehand.

Obama, responding to Clinton's interview, said: "One of the things that we've seen over the last several years is a bunch of talk using words like 'obliterate'. It doesn't actually produce good results. And so I'm not interested in sabre-rattling."

Iran does not yet have a nuclear weapon and insists that its uranium enrichment programme, which could be used to build a nuclear weapon, is purely for civilian purposes. Israel has hinted it may attack Iranian nuclear sites to prevent it acquiring a nuclear weapon, and Iran has said it would retaliate.