OAK BLUFFS, Massachusetts - A "heartbroken" President Barack Obama Wednesday lauded Senator Edward Kennedy as a "singular figure in American history" after the Democratic icon died of cancer, ending an epic era in US politics.

The president, who considered Kennedy a friend and political mentor, praised him as a fearless defender of the American dream who had touched countless lives with his full-throated support of liberal causes.

"Even though we knew this day was coming for some time now, we awaited it with no small amount of dread," Obama said, at a farm he is renting on the east coast island of Martha's Vineyard during his week-long vacation.

"The outpouring of love, gratitude and fond memories which we have all witnessed is a testimony to the way this singular figure in American history touched so many lives."

Obama poignantly compared the long life of Edward Kennedy, who died aged 77, with the violent deaths of his brothers, ex-president John Kennedy and presidential hopeful Robert Kennedy, who were cut down by assassins' bullets.

"His fight has given us the opportunity we were denied when his brothers John and Robert were taken from us: the blessing of time to say thank you and goodbye," Obama said.

"For his family, he was a guardian. For America, he was a defender of a dream," Obama said, adding that he had spoken to Kennedy's widow, Vicki, about his "extraordinary life" on Wednesday morning.

Earlier, in a written statement issued within hours of Kennedy's death at his home in Hyannis Port, just across Nantucket Sound from where the Obamas were staying, the president said he and his wife, Michelle, were "heartbroken."

"An important chapter in our history has come to an end. Our country has lost a great leader, who picked up the torch of his fallen brothers and became the greatest United States Senator of our time."

"For five decades, virtually every major piece of legislation to advance the civil rights, health and economic well being of the American people bore his name and resulted from his efforts," Obama said.

Obama, the first African-American president, said that Kennedy's crusade for equality had helped many of his countrymen pursue their dreams, including himself.

Kennedy passed away at the moment when his skills as a Senate dealmaker were most needed as the president struggles to enact an ambitious health care reform plan -- an issue for which Kennedy fought for decades.

"I valued his wise counsel in the Senate, where, regardless of the swirl of events, he always had time for a new colleague," said Obama, a former senator himself.

"I cherished his confidence and momentous support in my race for the presidency," Obama added, noting that Kennedy broke with former allies Hillary and Bill Clinton to make an early endorsement of his run for the White House.

At the time, the move was seen as an important validation of Obama's candidacy, and the passing of the torch from the brother of the assassinated political legends to a young and charismatic liberal champion.

Kennedy made a poignant farewell appearance at the Democratic National convention a year ago in Denver to endorse Obama, reprising his famous 1980 speech after his own failed presidential campaign.

"This November, the torch will be passed again to a new generation of Americans, so with Barack Obama, and for you, and me, our country will be committed to his cause," Kennedy roared.

"The work will begin anew, the hope will rise again, and the dream lives on."

Earlier this month, Obama awarded America's highest civilian honor -- the Presidential Medal of Freedom -- to Kennedy, in a White House ceremony, though the legendary senator was too ill to be present.

"The life of Senator Edward M. Kennedy has made a difference for us all," Obama said, as he handed the award to Kennedy's daughter Kara.

White House officials had fielded repeated questions during Obama's vacation, which began Sunday, about whether the president would make a trip to see Kennedy at his home.

The fact no visit was planned hinted at the Senate giant's fragile state.