In this July 19, 2006, file photo Hillary Rodham Clinton speaks with Sen. Barack Obama (right) during the annual convention of the National Association for the Advancement of Colored People in Washington. (Photo: chinadaily.com.cn)

As Barack Obama basks in his historic accomplishment as the first black US presidential nominee, Hillary Clinton ends her groundbreaking effort as the first woman to go as far as she did in the quest for the White House.

Clinton plans to host a rally for supporters on Saturday where she will formally drop out of the contest and throw her support behind her rival of the last 16 months.

Obama, the senator from Illinois, clinched the Democratic nomination on Tuesday when a number of superdelegates, who can back any candidate, flocked to his camp.

"On Saturday, I will extend my congratulations to Senator Obama and my support for his candidacy," Clinton said in an e-mail to supporters.

"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."

Obama is not slated to appear at the rally at noon in Washington, but the extent of Clinton's endorsement will be of keen interest to the Obama camp. She won more than 17 million voters during the Democratic battle, and Obama will need many of those to defeat Republican John McCain in November.

(Xinhua News Agency June 7, 2008)