Nagasaki marked the 65th anniversary of the US atomic bombing of the Japanese port city on Monday, in which about 74,000 people were killed.
The ceremony observed a minute of silence in memory of victims of the attack at 11.02 am 65 years ago.
The Peace Memorial Ceremony was attended by a record 32 countries, including nuclear power Britain and France, which joined in for the first time. Both also attended events in Hiroshima last week.
The bombing, the second in the closing days of World War II, injured about the same number in Nagasaki, which had a population at the time of 240,000.
Nagasaki is now a prosperous city with a population of more than 440,000 on the southern Japanese island of Kyushu.
Three days after the atomic bombing of Hiroshima, the second blast increased the pressure for Japan to surrender, which it did on Aug 15, 1945, six days later.
UN Secretary General Ban Ki-moon met victims of the bombing Thursday during his first visit to Nagasaki. On Friday, Ban attended the ceremony in Hiroshima that commemorated the August 6, 1945 bombing of that western Japanese city. He was the first UN chief to participate in the annual event.
Representatives from more than 70 countries, including US Ambassador to Japan John Roos, attended Friday's ceremony in Hiroshima. Roos was the first US envoy to do so.