The statement included no details of their talks, as pressure mounted for Obama to invite Clinton to become his running mate.
Robert Gibbs, an Obama spokesman, would not say where the former rivals met, except that it was not at Clinton's home in Washington, as had been widely reported.
Reporters traveling with Obama sensed something might be happening between the pair when they arrived at Dulles International Airport after an event in Northern Virginia and Obama was not aboard the airplane.
Asked at the time about the Illinois senator's whereabouts, Gibbs smiled and declined to comment.
Clinton returned to Washington after the last primaries on Tuesday night, when Obama earned the 2,118 delegates he needed to secure the Democratic nomination. She planned to announce Saturday that she was ending her campaign and supporting Obama.
The meeting followed Clinton's disavowal hours earlier of efforts by some supporters who have urged Obama to choose her as his running mate.
"She is not seeking the vice presidency, and no one speaks for her but her," communications director Howard Wolfson said. "The choice here is Senator Obama's and his alone."
Even as Clinton was bowing out of the race, supporters in Congress and elsewhere were ramping up a campaign to pressure him to put her on the ticket.
Bob Johnson, the billionaire founder of Black Entertainment Television and a Clinton supporter, on Wednesday sent a letter to the Congressional Black Caucus urging the group to encourage Obama to choose Clinton as his No. 2. Johnson said he was doing so with her blessing.
Obama is seeking to become the first black president.
Clinton has told other friends and supporters she would be willing to be Obama's running mate. But her immediate task is bringing her own presidential bid to a close, and how.
In an e-mail to supporters, the New York senator said she "will be speaking on Saturday about how together we can rally the party behind Senator Obama. The stakes are too high and the task before us too important to do otherwise."
Clinton expressed the same sentiment in a conference call with 40 members of her national finance committee, whom she urged to begin raising money for Obama and for the Democratic National Committee.
"She was in good spirits and totally supportive, without qualification, of Senator Obama and his campaign," finance co-chairman Alan Patricof said of the call.
It was a shift in tone by the former first lady, who announced 17 months ago that she was "in it to win it." Many of her supporters want her as the vice presidential candidate, in their minds a "dream ticket" that would bring Obama her enthusiastic legions and broaden his appeal to white and working-class voters.
On his campaign plane Thursday, Obama praised Clinton for inspiring millions of voters and said she had opened the doors for his two young daughters to imagine being president one day.
"We're going to speak to them but also listen to them and get advice," he said of Clinton's campaign team.
Obama also said he would welcome help from former President Clinton, calling him an "enormous talent."
Obama indicated he intends to take his time making a decision about inviting Hillary Clinton to join the ticket.
"We're not going to be rushed into it. I don't think Senator Clinton expects a quick decision and I don't even know that she's necessarily interested in that," Obama told NBC in an interview.
Clinton's move to formally declare that she is backing the Illinois senator came after Democratic congressional colleagues made clear they had no stomach for a protracted intraparty battle. Now that Obama has the delegates needed for the nomination, Clinton had little choice but to end her quest.
Some of her closest supporters - the nearly two dozen House Democrats from her home state of New York - switched their endorsements to Obama Thursday. Their public announcement followed two days of private phone calls weighing her options.
"She was just as spunky as ever," Rep. Charlie Rangel said of Clinton's mood on the calls, as her friends and supporters urged her to come to a decision "sooner rather than later."
Many of the lawmakers said it was important for them, as New Yorkers who are close to Clinton and helped launch her presidential bid, to work together to repair some of the rifts in the party.