Barack Obama has been nominated as the Democratic Party�s presidential candidate.

Barack Obama has been nominated as the Democratic Party's presidential candidate.

His former rival Hillary Clinton called for the roll call of votes to be suspended and for Mr Obama to be nominated by acclamation during the party's national convention in Denver, Colorado.

The former first lady said she was acting "in the spirit of unity".

The 47-year-old Illinois senator is the first African American to become the presidential nominee of a major party.

She said: "On behalf of the great state of New York, with appreciation for the spirit and dedication of all who are gathered here, with eyes firmly fixed on the future, in the spirit of unity, with the goal of victory, with faith in our party and our country, let's declare together, in one voice, right here, right now, that Barack Obama is our candidate and he will be our president."

The auditorium erupted in cheers and a resounding "aye". Several delegates were in tears.

Earlier Bill Clinton sought to steel Democratic hearts with a rallying call by insisting America simply could not risk four more years of Bush-branded Republicanism under the stewardship of John McCain.

As delegates, voters and media commentators alike pore over the tone and content of his support for Barack Obama, they will watch for any recurrent sign of the bitterness the ex-President felt over the Obama camp's treatment of his wife in the bruising candidates' race.

Mr Clinton was expected to take to the podium in the Pepsi Centre and give a trademark rousing performance that, as the former First Lady sought to do the night before, was aimed at bringing the Democratic family together.

One fear was that Mr Clinton's renowned charisma and oratory would overshadow the contribution of the keynote speaker Joe Biden, the vice presidential nominee, who was also expected to lay into Mr McCain and take the hands-on fight to the Republicans.

Mr Clinton, who has shown flashes of anger over what he felt were unfair attacks on his wife during the primaries, has so far given Mr Obama only tepid support since his wife ceded the race to the senator from Illinois in June.

"There is still work to do on the Bill Clinton front," noted Howard Wolfson, a former Hillary Clinton campaign strategist.

On Tuesday, the former president again muddied the waters with remarks that Republicans seized on and claimed questioned whether Mr Obama could be effective.

"Candidate X agrees with you on everything but you don't think that person can deliver on anything. Candidate Y disagrees with you on half the issues but you believe that on the other half the candidate will be able to deliver," Mr Clinton said.

In the US media, he is sometimes known as "the Big Dog" after he capped a comeback in his 1992 presidential campaign by promising to fight for New Hampshire voters "until the last dog dies."

Some Democratic delegates at the convention were adamant that in the final analysis the Big Dog would bark loudly for Mr Obama.

"Bill Clinton's feelings are hurt. His ego is bruised," said Brandon Hines, who, at 20, is Michigan's youngest delegate. Yet, he added: "He will come around for Obama."

The ex-president was due to speak shortly after his wife's name was symbolically nominated, a way of honouring her and placating her loyal band of supporters.

Yet, there were fears in the Obama camp that any floor demonstration for his defeated rival could be a blot on the party's hopes of showing a unified front against the Republicans.

Yesterday, Mr McCain continued his negative campaigning. A new TV advert said Mr Obama was "dangerously unprepared" for the White House when he described Iran as a "tiny" nation that did not pose a serious threat.