Hiroshima commemorates 72nd anniversary of atomic bombing with a gathering at the city's Peace Memorial Park. (Xinhua/Ma Ping)

HIROSHIMA, Japan, Aug. 6 (Xinhua) -- Hiroshima, the city that suffered U.S. atomic bombing in 1945 during World War II, commemorated the 72nd anniversary of the tragedy on Sunday at the city's Peace Memorial Park, with its mayor calling for peace and a world free of nuclear weapons.

Over 50,000 people attended the ceremony, including survivors of the attack, their descendants, peace activists and representatives from some 80 countries and regions.

Kazumi Matsui, mayor of the city, made a peace declaration to the audience. He mentioned the loss of lives and culture and the sufferings caused by the atomic bombing and urged the Japanese government to "do all in its power" to facilitate a nuclear weapon-free world.

He also urged the government to give more support to the surviving victims of the 1945 atomic bombings and " many others who also suffered mentally and physically from the effects of radiation."

Hiroshima commemorates 72nd anniversary of atomic bombing with students praying for the victims of the tragedy. (Xinhua/Ma Ping)

Japanese Prime Minister Shinzo Abe delivered a speech at the ceremony, in which he made no mention of the historical background for the atomic bombings or Japan's aggressive war against its neighbors.

"By firmly maintaining our three non-nuclear principles (of not producing, possessing or allowing nuclear weapons on Japanese territory) and continuing to appeal to both nuclear and non-nuclear states, Japan is determined to lead the international community," he said.

Hiroshima commemorates 72nd anniversary of atomic bombing while People holding banners protest Japanese Prime Minister Shinzo Abe's plan to revise the pacifist Constitution. (Xinhua/Ma Ping)

While Abe spoke, shouts of protest rang out from around the park, protesting against the prime minister's long-held ambition of revising the pacifist Constitution and other policies that they say could bring Japan to war, as well as the recent scandals that have plunged Abe's approval rating.

Hundreds of protesters gathered around the park, holding banners and shouting slogans such as "Oppose war and Constitution revision" and "Abe shall step down."

"I'm against Abe attending this ceremony, for his administration only protects the interests of some people and he tries to revise the pacifist Constitution and could drag Japan into war," said Takehiko Matsumoto, a protester from Sendai.

To accelerate Japan's surrender in the WWII, the U.S. forces dropped two atomic bombs on Hiroshima and Nagasaki respectively on Aug. 6 and Aug. 9, 1945. Japan surrendered to the Allied Forces on Aug. 15, 1945, bringing an end to WWII.