Barack Obama began campaigning with full force in New Hampshire today after storming to victory in the Iowa caucuses last night.

The Illinois senator pushed Hillary Clinton into third place in the opening contest of the 2008 Democratic presidential race, which he declared had been a "defining moment in history" for America.

In a rally in Portsmouth, New Hampshire, this morning, Mr Obama told his screaming supporters that they had a chance to change their country.

"New Hampshire," he told them, "in four days, you can change America.

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"In four days, you can do what Iowa did last night, and what America could do next year."

He said he would not be changing his campaign strategy for the new state: "It's not broken. Why fix it?"

Another win in New Hampshire's primary on Tuesday could provide Mr Obama with the momentum needed to propel him all the way to the White House.

In Iowa last night Mr Obama won 38 per cent of elected delegates after a record turnout boosted by independent and young idealistic voters. Mrs Clinton secured 29 per cent of delegates, fractionally behind John Edwards.

She has consistently led national opinion polls for the Democratic nomination and in a concession speech last night insisted she was ready for the next stage of a contest, saying she was "a candidate who will be ready to go the distance".

She left Iowa at midnight last night to begin campaigning in Nashua, New Hampshire, where, joined by her husband in a state that revived Bill Clinton's run for the Democratic nomination in 1992, Mrs Clinton answered questions about American troop withdrawal and health care.

She pledged to begin to withdraw all American troops from Iraq "as soon as I possibly can".

"I'm running for President and as President, I want you to know that I am going to protect the lives of American citizens," she said.

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