Mayor Kazumi Matsui urged world leaders to more seriously commit to nuclear disarmament, pointing out Japan's failures.
"I ask the Japanese government to heed the appeal of the (bombing survivors) to sign, ratify and become a party to the Treaty on the Prohibition of Nuclear Weapons," Matsui said in his peace declaration.
"As the only nation to suffer a nuclear attack, Japan must persuade the global public to unite with the spirit of Hiroshima."
His speech highlights what survivors feel is the hypocrisy of Japan's government, which hosts 50,000 American troops and is protected by the US nuclear umbrella.
Tokyo has not signed the nuclear weapons ban treaty adopted in 2017, despite its non-nuclear pledge, a failure to act that atomic bombing survivors and pacifist groups call insincere.
The US dropped its first atomic bomb on Hiroshima on August 6, 1945, destroying the city and killing 140,000 people.
The US dropped a second bomb three days later on Nagasaki, killing another 70,000. Japan surrendered August 15, ending World War II and its nearly half-century of aggression in Asia.
Survivors, their relatives and other participants marked the 8:15 am blast anniversary with a minute of silence.
Thursday's peace ceremony at the Hiroshima Peace Memorial Park was scaled down because of the coronavirus pandemic.
The fewer than 1,000 attendees was one-tenth of those attending in past years.
Some survivors and their relatives prayed at the park's cenotaph before the ceremony. The registry of the atomic bombing victims is stored at the cenotaph, whose inscription reads "Let all the souls here rest in peace for we shall not repeat the mistake."
Prime Minister Shinzo Abe, in his speech at the ceremony, said Japan is committed to nuclear weapons ban but a nuclear free world cannot be achieved overnight and that it has to start from dialogue between opposite sides.
"Japan's position is to serve as a bridge between different sides and patiently promote their dialogue and actions to achieve a world without nuclear weapons," Abe said. Nuclear policies are divided amid a harsh security environment, so it is necessary to create common ground first, he said.
An aging group of survivors, known as hibakusha, feel a growing urgency to tell their stories, in hopes of reaching a younger generation.
On the 75th anniversary, elderly survivors, whose average age now exceeds 83, lamented the slow progress of nuclear disarmament.
They expressed anger over what they said was the Japanese government's reluctance to help and listen to those who suffered from the atomic bombing.
"Abe's words and actions don't seem to match," said Manabu Iwasa, 47, who came to the park to pray for his father, a survivor who died at age 87 in March.
"Japan apparently sides with the U.S. and make more effort toward nuclear weapons ban," he said.
"It's frustrating, but there is not much we individuals can do."
Keiko Ogura, 84, who survived the atomic bombing at age 8, wants non-nuclear states to pressure Japan into signing the nuclear weapons prohibition treaty.
"Many survivors are offended by the prime minister of this country who does not sign the nuclear weapons prohibition treaty," she said.
Matsui urged world leaders, especially those from nuclear weapons states, to visit Hiroshima and see the reality of the atomic bombing.