Obama wins backing of Bill Clinton

Mr Clinton said the often bitter primary battle between his wife Hillary and Mr Obama for the Democratic Party's presidential nomination "created so much heat it increased global warming".

But he said the contest had strengthened the Illinois senator and he was "ready to be president of the United States".

In a prime-time speech at the party's national convention in Denver, Colorado, Mr Clinton laid out a series of reasons why he was now backing Mr Obama and said America was in trouble on two fronts.

"The American dream is under siege at home and America's leadership in the world has been weakened," he said. "Everything I learned in my eight years as president, and in the work I have done since in America and across the globe, has convinced me that Barack Obama is the man for this job.

"He has a remarkable ability to inspire people, to raise our hopes and rally us to high purpose. His policies on the economy, on taxes, on healthcare, on energy are far superior to the Republican alternative.

"With running mate Joe Biden's experience and wisdom supporting Barack Obama's proven understanding, instincts and insight, America will have the national security leadership we need.

Mr Clinton said Republicans had called him "too young and too inexperienced to be commander in chief" when he ran for the presidency aged 45 in 1992 - the same criticisms which are now being used against Mr Obama.

"It didn't work in 1992 because we were on the right side of history," he said. "And it will not work in 2008 because Barack Obama is on the right side of history."

He went on: "Barack Obama will lead us away from the division and fear of the last eight years, back to unity and hope."