In a bid to put up a united front, presumptive Democratic presidential candidate Barack Obama had a closely wrapped meeting with his vanquished rival Hillary Clinton hours after she announced her decision to bow out of the race following a 17-month acrimonious campaign.

While aides kept the media at bay, a joint statement by the two campaigns said they had "productive discussions about important work that needs to be done to succeed in November" presidential elections in which Obama faces Republican candidate John McCain.

Though there is intense speculation about a Clinton-Obama "dream ticket", the campaigns gave no other details of the meeting which was held after a day-long campaign by Obama in the Republican strong hold of Virginia.

But some officials said the meeting was initiated by Clinton and that two had asked their aides not disclose the contents or venue of the meeting.

The first hint about the meeting came when Obama failed to travel with reporters and his aides on the campaign plane to Chicago.

Obama and Clinton apparently did not want to disclose the location of their meeting to avoid being questioned by media.

A buzz that they are meeting in Clinton's Washington home led to dozens of reporters and camera crews being stationed there but the only report they could give was about security around the residence and the rooms in which lights were on.

Obama's spokesman Robert Gibbs said that the two leaders had met but denied the site was Clinton's house.