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Hillary Clinton today threatened to “obliterate” Iran if it launched a nuclear attack on Israel, her most aggressive rhetoric yet against Tehran as she seeks to cast doubts on whether Barack Obama would be a strong commander-in-chief.

Mrs Clinton made her remarks as a record number of primary voters descended on voting stations in Pennsylvania for its potentially pivotal primary, the first contest in her marathon nominating battle with Mr Obama for six weeks.

With Mr Obama reliant on a large African-American turnout in Philadelphia, where half the city’s registered Democrats are black, the issue of his multi-ethnic background was raised again after a claim by Bill Clinton that the Illinois senator’s campaign “played the race card on me”.

The former President was accused widely of trying to scare white voters away from Mr Obama when he said after the South Carolina primary that the Illinois senator’s victory there was akin to the 1984 win in the state by Jesse Jackson, the civil rights activist.

Mr Clinton told a Philadelphia radio station today that he was the victim of tactics designed to galvanise African-American voters to back Mr Obama. “And we know, from memos from the [Obama] campaign and everything, that they planned to do it all along.” After the interview ended, but still audible on the air, Mr Clinton said: “I don’t think I should take any s**t from anybody on that, do you?” – a clear sign of how his loss of once-beloved status among parts of the black community has stung him.

Mr Obama responded. “So, former President Clinton dismissed my victory in South Carolina as being similar to Jesse Jackson, and he’s suggesting that somehow I had something to do with it? I have no idea what he meant.”

Mrs Clinton, who on Monday released a television commercial using images of Osama bin Laden that ended with the question “Who do you think has what it takes?” made her comments about Iran during an interview with ABC.

“I want the Iranians to know that if I’m the president, we will attack Iran,” she said after being asked what she would do if Iran launched a nuclear attack on Israel. “In the next ten years, during which they might foolishly consider launching an attack on Israel, we would be able to totally obliterate them.”

Mrs Clinton, who last month even said that John McCain, the Republican nominee-elect, was more qualified than Mr Obama to be commander-in-chief, appeared to be drawing a contrast between the Illinois senator’s stance on Iran. He has said he would open talks with the Iranian leadership.

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