John Kerry has become the first US secretary of state to pay his respects at Hiroshima's memorial to victims of the 1945 US nuclear attack, along with his counterparts from the Group of Seven advanced economies.
Following the visit, the ministers issued a statement on Monday reaffirming their commitment to building a world without nuclear arms, but said the push had been made more complex by North Korea's repeated provocations and by the worsening security in Syria and Ukraine.
Gathering in the Japanese city of Hiroshima where the US dropped an atomic bomb on August 6, 1945, the ministers also said they found it profoundly deplorable that North Korea had conducted four nuclear tests during the 21st century.
"We reaffirm our commitment to seeking a safer world for all and to creating the conditions for a world without nuclear weapons in a way that promotes international stability," they said in a written declaration on nuclear disarmament.
"This task is made more complex by the deteriorating security environment in a number of regions, such as Syria and Ukraine, and, in particular by North Korea's repeated provocations."
Earlier Kerry toured the Hiroshima Peace Memorial and Museum, whose haunting displays include photographs of badly burned victims, the tattered and stained clothes they wore and statues depicting them with flesh melting from their limbs.
The ministers from Britain, Canada, France, Germany, Italy, Japan and the US then laid white wreaths at a cenotaph to the victims of the bombing, which reduced the city to ashes and killed about 140,000 people by the end of that year.
"Everyone in the world should see and feel the power of this memorial. It is a stark, harsh, compelling reminder not only of our obligation to end the threat of nuclear weapons, but to rededicate all our effort to avoid war itself," Kerry wrote in a guest book.
After a moment of silence by the ministers, Japanese schoolchildren, who had lined the entrance waving flags of all the G7 nations, presented them with leis made of paper cranes, symbolising peace, in each country's national colours.
At Kerry's suggestion, the ministers also made an impromptu visit to the Atomic Bomb Dome, the skeletal remains of the only structure left standing near the hypocentre of the bomb explosion and now a UNESCO World Heritage site.
Three days after a US warplane dropped a nuclear bomb on Hiroshima, another atomic bomb was dropped on Nagasaki on August 9, 1945. Japan surrendered six days later.
Kerry's trip could pave the way for an unprecedented visit to Hiroshima by a sitting US president when Obama attends the annual G7 leaders summit in another Japanese city next month.
A visit could be controversial in America if it were viewed as an apology. A majority of Americans still view the bombings as justified to end the war and save US lives, while the vast majority of Japanese believe it was not justified.
The G7 foreign ministers' trip to the museum and memorial is part of Japan's effort to send a strong nuclear disarmament message from Hiroshima, the world's first city to suffer atomic bombing.
"I think this first-ever visit by G7 foreign ministers to the peace memorial park is a historic first step towards reviving momentum toward a world without nuclear weapons," Japanese Foreign Minister Fumio Kishida said in a statement.
In a separate, detailed statement on maritime security, the G7 ministers voiced their strong opposition to provocative attempts to change the status quo in the East and South China Seas, an apparent reference to China, which is locked in territorial disputes with other nations including the Philippines, Vietnam and Japan.
