Former President Bill Clinton, center, waves as he arrives at the Democratic National Convention in Denver, 26 Aug 2008

Former U.S. President Bill Clinton will take the stage later Wednesday at the Democratic National Convention, a day after his wife issued a ringing endorsement for Democratic presidential candidate Barack Obama.

In a much-anticipated speech Tuesday, Senator Hillary Clinton described herself as "a proud supporter of Barack Obama" and urged her party to unite behind his candidacy.  The New York senator cautioned that, in her words, "we are on the same team, and none of us can sit on the sidelines".

Obama and his vice presidential running mate, Delaware Senator Joseph Biden, will be formally placed in nomination later Wednesday.  

Hillary Clinton's name will also be placed in nomination. Some state delegations will cast ballots in what is expected to be a largely symbolic roll call vote to determine the party's candidate.

Biden will deliver his acceptance speech after former president Clinton's address.  

Obama watched Senator Clinton's speech at the home of supporters in the western city of Billings, in the state of Montana.  He told reporters the speech was "outstanding."  A spokesman said he later called the Clintons to express his gratitude.

Obama would be the first African-American nominee of a major U.S. political party when he accepts the nomination Thursday, the final day of the convention.

Republicans hold their national convention next week in the city of St. Paul, Minnesota, where Senator John McCain is expected to be nominated.

Some information for this report was provided by AP.