Washington - Hillary Clinton's presidential campaign on Tuesday denied a report that she plans to acknowledge that rival Barack Obama has won enough delegates to secure the Democratic nomination.

Clinton campaign chairman Terry McAuliffe told CNN the story was "100 per cent" incorrect and that the former first lady intends to fight on until someone has captured the nomination.

"That is not at all what Senator Clinton is going to talk about tonight," McAuliffe said. "No one has the number to be the nominee of the Democratic party right now."

His comments come following a report, citing Clinton campaign officials, that the New York senator will admit Obama has won enough delegates after the final state primaries in South Dakota and Montana Tuesday night.

"They are 100 per cent reporting incorrectly," McAuliffe said, adding there will be "no surprises" in Clinton's speech after polls close.

Clinton slightly trails Obama in the delegate count determined by the outcome of state contests, but her chances of overtaking him have grown increasingly slim. Bill Clinton raised speculation that his wife was preparing to exit the race during a campaign rally Monday.

"This may be the last day I'm ever involved in a campaign of this kind," Bill Clinton said in South Dakota.

"I thought I was out of politics until Hillary decided to run. It has been one of the greatest honours of my life to go around and campaign for her for president," the former president said.

Obama has slowly neared taking a majority of delegates, and a good showing later Tuesday could allow him to claim the nomination. But Clinton believes she can persuade superdelegates, a group of Democratic party insiders who cast votes independently of the state- by-state process, that she is the best candidate to square off against Republican John McCain in the November 4 election.

A group of more than a dozen undecided Democratic senators reportedly met Monday in Washington to consider their options. The Washington Post Tuesday reported that the group may endorse Obama after polling stations close Tuesday evening in the two final states.

Clinton gained some last-minute momentum after trouncing Obama Sunday in Puerto Rico's primary. But the victory by 68 to 32 per cent could be Clinton's last, as Obama is favoured Tuesday in both Montana and South Dakota - the final events in the state-by-state intra-party contests that began on January 3 in Iowa. (dpa)