Edwards -- a former North Carolina U.S. senator who was John Kerry's running mate on the 2004 Democratic ticket -- announced his endorsement at an Obama campaign rally in Grand Rapids, Mich., telling the audience the race for the Democratic presidential nomination is down to "two amazing candidates."

The crowd booed when Edwards mentioned the name of Clinton, the New York senator who has remained in the race despite long odds that she can win the nomination over Obama.

Edwards praised Clinton both on her record in office and her presidential campaign.

"What she has shown is strength and character," he said.

"We are a stronger party because Hillary Clinton is a Democrat," said Edwards, "And we're going to have a stronger presidential nominee in the fall because of her work."

Edwards ended his second quest for the presidential nomination Jan. 30. He had won more than 20 pledged delegates to the party's Denver convention in August when he dropped out -- and could ask them to back Obama, CNN reported Wednesday.

In recent interviews, Edwards had refused to endorse either Clinton or Obama, saying he was unsure whether his endorsement would matter. Edwards had urged both remaining contenders to make ending poverty a central issue of the general election campaign.