Kerry, who was accompanied by other G7 foreign ministers, is the highest-ranking administration official to pay his respects at the revered site of the World War II bombing -- the world's first nuclear attack.
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His trip comes as White House officials say President Barack Obama is considering a stop in the city late next month around the time of a Group of Seven summit, which is being held in another part of the country.
Kerry's visit, and speculation that Obama may also go to Hiroshima, have prompted suggestions that Washington may be considering an official apology over the August 1945 bombing, which killed 140,000 people.
Kerry and other officials, however, have played down that expectation.
"My visit to Hiroshima has very special meaning about the strength of our relationship and the journey we have travelled together since the difficult time of the war," Kerry told Japanese foreign minister Fumio Kishida on Monday ahead of the memorial visit.
He added, "We will revisit the past and honour those who perished, (but) this trip is not about the past; it's about the present and the future."
Separately, a US official said flatly that Kerry would offer no formal apology.
"If you are asking whether the secretary of state came to Hiroshima to apologise, the answer is no," the State Department official, who asked not to be named, told reporters travelling with Kerry late Sunday.
Arriving under tight security, the G7 ministers and the foreign policy chief of the European Union started their visit at a museum that shows the devastating impact of the bombing -- such as survivors' burned clothing and other personal affects.
They then laid individual floral wreaths at a cenotaph in the leafy park next to the museum.
Many were killed instantly when the bomb was dropped, creating a firestorm that flattened swathes of the city. Thousands of others died later from severe radiation exposure.
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On August 9, 1945, three days later, another US atomic bomb exploded over the city of Nagasaki, killing some 74,000 people. Less than a week later, on August 15, Emperor Hirohito announced Japan's surrender, ending World War II.
The issue of the bombings is a highly emotive one in both Japan and the United States.
Japan, as the only nation to have experienced a nuclear attack, emphasises the suffering its people endured. But while publicly calling for the eradication of nuclear weapons, it has for decades been a close security ally of Washington under the protection of the US nuclear umbrella.
Many in the US, meanwhile, chafe at the suggestion of an apology, saying that Japan started the war with its attack on Pearl Harbor and argue that the atomic bombings hastened the war's end, thus preventing greater casualties.
In 2008, Nancy Pelosi, the then speaker of the US House of Representatives and third in the line of presidential succession, visited Hiroshima.
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Among other G7 foreign ministers set to visit the memorial Monday are Britain's Philip Hammond and France's Jean-Marc Ayrault. It also marks the first time that top diplomats from the two nuclear-armed countries are visiting the city.
The group journey to the memorial comes as the ministers wrap up their final day of meetings with discussions focused on global hotspot issues including terrorism and other security threats as well as instability in the Middle East and elsewhere.
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