Democratic presidential candidate Barack Obama has paid tribute to Hillary Clinton for her “valiant campaign” after she endorsed him and urged her supporters to unite behind his candidacy.
Speaking after Mrs Clinton formally abandoned her bid for the nomination, Mr Obama said his former rival had “shattered barriers on behalf of my daughters and women everywhere”.
“Our party and our country are stronger because of the work she has done throughout her life, and I'm a better candidate for having had the privilege of competing with her,” Mr Obama said in a statement.
Mrs Clinton formally suspended her 16-month-long campaign with a speech at the National Building Museum in Washington saying she would work hard to put Mr Obama in the White House.
She said Mr Obama had proved his "grace and grit", and she urged her supporters to put their energy into electing him.
Mr Obama will face the Republican presumptive nominee, John McCain, in November's presidential election.
“I will work my heart out to make sure that Senator Obama is our next president,” Ms Clinton told a crowd of about 2,000 at the National Building Museum in Washington. “I ask all of you to join me in working as hard for Barack Obama as you have for me."
US Democratic presidential candidate Senator Hillary Clinton announcing her endorsement of Barack Obama at the National Building Museum in Washington last night. Seated on the right are her daughter, Chelsea and husband, former US President Bill Clinton
With her husband, former President Bill Clinton, and her daughter, Chelsea, standing to the side of the stage, Ms Clinton said she and Mr Obama shared the same values and goals.
"I endorse him and I throw my full support behind him," she said. "We will make history together." In a statement later, Mr Obama said he was "thrilled" to have Mrs Clinton's endorsement.
He credited her with reaching out to many American voters and making him a stronger candidate and said in a statement he was "thrilled" to have Mrs Clinton's endorsement.
"She inspired millions with her strength, courage and unyielding commitment to the cause of working Americans."
Mr Obama also suggested that Mrs Clinton would continue to play a significant role in American politics but did not hint whether that would included her being his running mate.
"No one knows better than Senator Clinton how desperately America and the American people need change, and I know she will continue to be in the forefront of that battle this fall and for years to come."
Ms Clinton, a New York senator and former first lady, was once the heavy favourite to become the first female US president. She had resisted calls to pull out of the race for months as the split between their supporters grew wider.
"This has been a tough fight, but the Democratic Party is a family, and now it's time to restore the ties that bind us together and to come together," she said.
Ms Clinton's decision to suspend her campaign rather than formally disband it means she retains some control of her delegates and can still work to repay more than $20 million in campaign debt, including more than $11 million she loaned the campaign from her own pocket.