Bells have tolled in Hiroshima, Japan as the city marked the 77th anniversary of the world's first atomic bombing.
United Nations Secretary General Antonio Guterres joined the thousands of people packed into the Peace Park in the centre of the city to mark the anniversary of the bombing that killed 140,000 before the end of 1945, only the second time a UN secretary general has taken part in the annual ceremony.
"Nuclear weapons are nonsense. They guarantee no safety - only death and destruction," Guterres said.
"Three quarters of a century later, we must ask what we've learned from the mushroom cloud that swelled above this city in 1945."
Guterres sidestepped a direct mention of Russia, which calls its invasion of Ukraine a "special military operation."
At 8.15am on August 6, 1945, the US B-29 warplane Enola Gay dropped a bomb nicknamed Little Boy and obliterated the city with an estimated population of 350,000. Thousands more died later from injuries and radiation-related illnesses.
On Saturday, as cicadas shrilled in the heavy summer air, the Peace Bell sounded and the crowd, including Prime Minister Fumio Kishida, who is from Hiroshima, observed a moment of silence at the exact time the bomb exploded.
On Thursday, Russian ambassador to Japan Mikhail Galuzin offered flowers at a memorial stone in the park and told reporters his nation would never use nuclear weapons.
Kishida, who has chosen Hiroshima as the site of next year's Group of Seven summit, called on the world to abandon nuclear weapons.
Earlier this week, he became the first Japanese leader to take part in the Review Conference of the Parties to the Treaty on the Non-Proliferation of Nuclear Weapons (NPT).
"We will continue towards the ideal of nuclear disarmament even given the current tough security environment," he said.
The Hiroshima catastrophe was followed by the US military's atomic bombing of Nagasaki on August 9, instantly killing more than 75,000 people.
Japan surrendered six days later, ending World War II.
Australian Associated Press