President Barack Obama called on nations to "escape the logic of fear" and reduce their stockpiles of nuclear weapons as he became the first sitting U.S. President to visit Hiroshima, Japan Friday.

Obama did not apologize for or second-guess President Harry Truman's decision to drop the atomic bombs on Hiroshima and Nagasaki in August 1945, accelerating the end of World War II.

But speaking in the place where the nuclear age began, Obama said the memory of the 140,000 people killed on Aug. 6, 1945, "must never fade ... We stand here in the middle of this city and force ourselves to imagine the moment the bomb fell ... we listen to a silent cry."

"Death fell from the sky and the world was changed," Obama said, adding that the destruction of Hiroshima "demonstrated that mankind possessed the means to destroy itself."

During his remarks, Obama included both South Koreans and American prisoners of war in recounting the death toll at Hiroshima -- a nod to advocates for both groups that publicly warned the president not to forget their dead. He spoke broadly of the brutality of the war that begat the bombing, but did not assign blame.

The president met Japanese Prime Minister Shinzo Abe at the Hiroshima Peace Memorial Museum, where he inscribed the guest book with this message: "We have known the agony of war. Let us now find the courage, together, to spread peace, and pursue a world without nuclear weapons."

Just before his speech, Obama laid a wreath near the base of the cenotaph, an arched monument in Hiroshima's Peace Memorial Park. The president closed his eyes and briefly bowed his head.

Abe called Obama's visit courageous and long-awaited. He said it would help the suffering of survivors and echoed the anti-nuclear sentiments.

"At any place in world, this tragedy must not be repeated again," Abe said.

After Obama and Abe spoke, the two leaders met briefly with survivors who were in the audience. One man stamped his cane emphatically while speaking to the president. Obama smiled as he listened.

Obama touched down in Hiroshima after completing talks with world leaders at an international summit in Shima, Japan.

In remarks earlier Friday to U.S. and Japanese troops at nearby Marine Corps Air Station Iwakuni, Obama said the visit was "an opportunity to honor the memory of all those who were lost in World War II", as well as "a chance to pursue peace and security."

The only other U.S. president to visit Hiroshima was Jimmy Carter, who did so in 1984, four years after being voted out of office. 

The Associated Press contributed to this report.