The event was aimed at shoring up party unity, following the hardest-fought Democratic Party primaries in decades.

Mr Obama announced that he would personally donate $2,300 (£1,160), the maximum amount allowed by law, to help cover Mrs Clinton's campaign debts.

He said he would call on his top financial backers to do the same.

Mr Obama received a standing ovation from a crowd of more than 200 at Washington's Mayflower Hotel when he said he would enlist his supporters to help pay off Mrs Clinton's debt.

Mrs Clinton is due to back Senator Obama's bid for the White House for the first time on Friday at a joint campaign rally in Unity, New Hampshire - where they each got 107 votes in the state's primary.

Reconciliation

Latest opinion polls suggest that while Mr Obama has made headway in winning over Mrs Clinton's supporters, one in five of them has indicated they will vote for the Republican candidate, John McCain.
I'm going to need Hillary by my side campaigning during this election, and I'm going to need all of you," Mr Obama told the Washington audience.

Mrs Clinton's advisers have warned Mr Obama that her ability to campaign on his behalf will be limited if she has to spend the summer raising money to pay off her more than $20m (£10m) debt racked up in her failed bid to win the nomination.

Mrs Clinton told her donors they must make electing Mr Obama a priority, as she acknowledged the often bitter fight between the two former rivals.

"This was a hard-fought campaign, that's what made it so exciting and intense and why people's passions ran so high on both sides," she said.

"I know my supporters have extremely strong feelings, and I know Barack's do as well. But we are a family, and we have an opportunity now to really demonstrate clearly we do know what's at stake, and we will do whatever it takes to win back this White House," she added.

Since Mrs Clinton suspended her campaign and endorsed Mr Obama, the former rivals have not met in person since they spoke at the Washington home of Senator Dianne Feinstein, two days after the last primaries.

BBC