TOKYO >> Japan marked the 67th anniversary of the world’s first atomic bomb attack with a ceremony today that was attended by a grandson of Harry Truman, the U.S. president who ordered the bomb dropped on Hiroshima.

About 50,000 people gathered in Hiroshima’s peace park near the epicenter of the 1945 blast that destroyed most of the city and killed as many as 140,000 people. A second atomic bombing Aug. 9 that year in Nagasaki killed tens of thousands more and prompted Japan to surrender to the World War II Allies.

The ceremony, attended by representatives of about 70 countries, began with the ringing of a temple bell and a moment of silence. Flowers were placed before Hiroshima’s eternal flame, which is the park’s centerpiece.

Truman’s grandson, Clifton Truman Daniel, and the grandson of a radar operator who was on both of the planes that dropped the atomic bombs, joined in the memorial. Ari Beser’s grandfather, Jacob Beser, was the only person who directly took part in both the Hiroshima and Nagasaki bombings.

In a news conference after the memorial, Daniel declined to comment on whether his grandfather’s decision was the right one.

“I’m two generations down the line. It’s now my responsibility to do all I can to make sure we never use nuclear weapons again,” he said, according to Japan’s Kyodo news service.

Daniel, 55, said earlier that he decided to visit Hiroshima and Nagasaki because he needed to know the consequences of his grandfather’s decision as part of his own efforts to help achieve a nuclear-free world.

The U.S. government sent a representative — the American ambassador — to the annual commemoration for the first time two years ago. Ambassador John Roos attended the Hiroshima ceremony today.