HIROSHIMA, Japan » Japan marked the 70th anniversary of the atomic bombing of Hiroshima on Thursday, with Mayor Kazumi Matsui renewing calls for U.S. President Barack Obama and other world leaders to step up efforts toward making a nuclear weapons free world.

Tens of thousands of attendants stood for a minute of silence at 8:30 a.m. at the ceremony in Hiroshima’s peace park near the epicenter of the 1945 attack, marking the moment of the atomic blast. The U.S. bomb, first one used at war, killed 140,000 people, and a second bombing, over Nagasaki three days later, killed another 70,000, prompting Japan’s surrender in World War II.

Matsui called the nuclear weapons "the ultimate inhumanity and evil" that must be abolished, and criticized nuclear powers for still using them as threats to achieve their national interests.

"We must establish a broad national security framework that does not rely on use of force but is based on trust," Matsui said. "Now is the time to take action."

He renewed an invitation to Obama and other world leaders to visit Hiroshima and Nagasaki to see the scars themselves.

With the average age of survivors now exceeding 80 years for the first time this year, passing on their stories is considered an urgent task.

Prime Minister Shinzo Abe said that as the sole country to face a nuclear attack, Japan had a duty to push for the elimination of nuclear weapons.

The anniversary comes as Japan is divided over Abe’s push to pass unpopular legislation to expand the country’s military role internationally.

Attendants this year included U.S. Ambassador Caroline Kennedy and representatives from more than 100 countries, including Britain, France and Russia.