Mr Obama paid tribute to Hillary Clinton, who is expected to bow out
Democratic hopeful Barack Obama has had an unannounced meeting with his defeated rival Hillary Clinton.
The talks came two days after Mr Obama in effect clinched the nomination for November's US presidential election.
A spokesman for Mr Obama said the two former opponents met to talk about bringing their campaigns together and uniting the party.
Mrs Clinton has distanced herself from reports that she was hoping to stand as a vice-presidential running mate.
The last-minute meeting in Washington came after Mr Obama spent the day campaigning in the Republican stronghold of Virginia - a signal that he is now targeting voters who might be drawn to Republican presumptive nominee John McCain.
Mr Obama held large rallies in the state.
The Illinois senator, under intense pressure from Clinton backers to choose her as his running mate, has announced a team to help him make his selection and said he will not be rushed.
Campaign aides said little about the meeting, which a Democratic source told ABC News was held at the Washington home of senior Democratic Senator Dianne Feinstein.
Hillary Clinton will thank her supporters on Saturday and endorse Obama
But reports say the two have put teams in place to handle communications between their respective camps in the coming days.
Senator Feinstein has said that a joint-ticket for the presidency would be a route to pulling together the pair's diverse constituencies.
On Tuesday Mrs Clinton said she would be "open" to the idea of being Mr Obama's running mate.
But a statement from the Clinton campaign on Thursday said: "While Senator Clinton has made clear throughout this process that she will do whatever she can to elect a Democrat to the White House, she is not seeking the vice presidency."
It adds: "The choice here is Senator Obama's and his alone."
The BBC's Andy Gallacher in Washington says that if Mr Obama were to choose her as his running mate, this could be seen as a tactical move to win over the almost 18m people who cast their votes for Senator Clinton.
But, our correspondent adds, Mr Obama has said it may be some time before he picks a running mate.
Earlier, in an email to supporters, Mrs Clinton said she would hold an event in Washington on Saturday to thank supporters and congratulate Mr Obama and extend her "support for his candidacy".
"This has been a long and hard-fought campaign, but as I have always said, my differences with Senator Obama are small compared to the differences we have with Senator McCain and the Republicans," she said.
"I will be speaking on Saturday about how together we can rally the party behind Senator Obama."
Since the close of the primary season on Tuesday, Mr Obama has paid tribute to Mrs Clinton and hinted that she would play a role in any future Obama administration.
At a rally in Bristow in northern Virginia on Thursday, he told a large crowd he was "a better candidate because of the work she did".
"Whatever differences exist between me and Hillary Clinton, they pale into insignificance in comparison with those that exist between us and the other side," he added.
Correspondents say Democrats sense an opportunity in Virginia, despite the 44 years since one of their nominees won the state in a presidential election.
Mr McCain has challenged Mr Obama to take part in debates in 10 town hall meetings before the Democratic convention in August. The Obama team is said to be considering the invitation.