WASHINGTON -- President Barack Obama on Thursday called Nelson Mandela's life and legacy a touchstone for him and an example "that all humanity should aspire to."
"We will not likely see the likes of Nelson Mandela again," Mr. Obama said at the White House, reacting to the death of the iconic South African statesman.
Mr. Obama probably will travel to South Africa for services for Mr. Mandela, according to a person familiar with White House planning who asked for anonymity because the trip hasn't been announced. The president ordered U.S. flags to be lowered to half-staff until sunset Monday in Mr. Mandela's honor, according to a White House proclamation.
Mr. Obama joined leaders worldwide in paying tribute to Mr. Mandela.
U.N. Secretary-General Ban Ki-moon said Mr. Mandela was "a giant for justice" who inspired people to fight for a better world. In 2009, the United Nations passed a resolution marking July 18 as Nelson Mandela International Day.
"No one did more in our time to advance the values and aspirations of the United Nations," Mr. Ban said. "Let us continue each day to be inspired by Nelson Mandela's lifelong example to keep working for a better and more just world."
On Thursday, The U.N. Security Council interrupted a meeting on the tribunals for former Yugoslavia and Rwanda and stood for a minute in silent tribute to Mr. Mandela.
Former U.N. Secretary-General Kofi Annan said the world had lost "a visionary leader, a courageous voice for justice and a clear moral compass." Both Mr. Annan and Archbishop Desmond Tutu were part of Mr. Mandela's group of statesmen known as The Elders.
"God was so good to us in South Africa by giving us Nelson Mandela to be our president at a crucial moment in our history," Archbishop Tutu said. "He inspired us to walk the path of forgiveness and reconciliation and so South Africa did not go up in flames."
Britain's Prime Minister David Cameron said "a great light has gone out in the world."
"My heart goes out to his family, and to all in South Africa and around the world whose lives were changed through his courage," Mr. Cameron said in a statement.
Japan's Prime Minister Shinzo Abe praised Mr. Mandela for setting an example of forgiveness. "After he succeeded in abolishing apartheid following a long struggle, he did not seek revenge, but took the lead in national reconciliation," Mr. Abe said.
Former President Bill Clinton said Mr. Mandela will be remembered "as a man of uncommon grace and compassion, for whom abandoning bitterness and embracing adversaries was not just a political strategy but a way of life."
Former President George H.W. Bush said Mr. Mandela was one of the greatest believers in freedom he had known.
"He was a man of tremendous moral courage, who changed the course in his country," Mr. Bush said.
Mr. Obama, the first black U.S. president, said during his White House remarks that he was "one of the countless millions who drew inspiration from Mandela's life. So long as I live, I will do what I can to learn from him."
Mr. Obama reflected on Mr. Mandela's achievement in standing up to the apartheid government of South Africa, going to jail and emerging to continue a quest for reconciliation and equality.
"His commitment to transfer power and reconcile with those who jailed him set an example that all humanity should aspire to, whether in the lives of nations or our own personal lives," the president said. "He achieved more than can be expected of any man."
Mr. Obama also spoke by phone Thursday night with South Africa's President Jacob Zuma to offer condolences and convey "how profoundly Mandela's extraordinary example of moral courage, kindness and humility influenced his own life," the White House said in a statement. Mr. Obama also reaffirmed the "strong and historic partnership" between the two countries, the White House said.
Mr. Obama's admiration for Mr. Mandela was evident during the president's trip to Africa in June.
Throughout his stops in Senegal, South Africa and Tanzania, Mr. Obama repeatedly reflected on the legacy of the man whom he has credited with influencing his own political ambitions and sense of activism.
While his aides had considered arranging a meeting between the first black presidents of the U.S. and South Africa, Mr. Mandela's health prevented a face-to-face session. Mr. Obama met with members of the Mandela family and spoke on the telephone with his wife, Graca Machel.
Mr. Obama and his wife, Michelle, brought daughters Sasha and Malia to Robben Island during the visit, to tour the lime quarry where Mr. Mandela labored as a prisoner and to stand in his apartheid-era cell.
Mr. Obama met Mr. Mandela just once, as a U.S. senator in 2005 at a Washington hotel.
Associated Press contributed.