Hillary Clinton has urged Democrat supporters to unite behind Barack Obama’s presidential bid during a key speech to the party convention in Denver.

Hillary Clinton was greeted with wild applause

Senator Clinton was hot favourite to win the Democratic nomination for the presidency, but Senator Obama overtook her to claim a narrow victory in the primaries following a bitterly-fought campaign.

Many observers believe that winning over the millions of Clinton supporters is crucial if Mr Obama is to beat John McCain. 

However, vocal groups of her fans remain unconvinced, with some saying they would prefer to vote Republican than Obama.

Taking to the stage after an introduction by her daughter, Chelsea, she was greeted with wild applause from the crowd, among whom her husband, former president Bill, was watching with tears in his eyes.

“Whether you voted for me, or you voted for Barack, the time is now to unite as a single party with a single purpose,” she said.

She said that America should not “suffer” four more years of Republican government and urged her supporters to throw their weight behind her former rival.

“No way, no how, no McCain,” she continued.

“Barack Obama is my candidate, and he must be our President.”

She also paid tribute to Joe Biden, Mr Obama’s choice as vice-presidential candidate - a significant gesture, because many thought she would get the job - and Mr Obama’s wife, Michelle.

Mr Obama, who watched the speech on television, hailed it as “outstanding”.

“That was excellent, that was a strong speech,” he added.

“She made the case for why we’re going to be unified in November and why we’re going to win this election.”

Sky News’ Jeremy Thompson, who is presenting from the convention, said: “It was an unequivocal endorsement of Barack Obama from Hillary Clinton - he couldn’t have asked for more from her.

“All eyes were on her - it was the biggest moment of the convention so far and could have been a make-or-break moment for Mr Obama.”

Sky News political analyst Jon-Christopher Bua added: “This was a tough one for Hillary and I think she did a masterful job.

“I think it took a lot of courage, strength and intelligence.”

Earlier, speakers on the second day of the convention repeatedly mentioned Mr Obama’s plan to revitalise the economy by creating five million new jobs.

They attacked Mr McCain as a rich elitist fond of “country-club economics” who would simply carry on George W Bush’s policies.

Several listed the country’s recent struggles with rising fuel and food prices before adding that it “could not afford” four more years of Republican government.

Before the main speeches got under way police said there was “insufficient evidence” to charge three men who were allegedly planning to assassinate Barack Obama.