US Secretary of State John Kerry has made a historic visit to Hiroshima's Peace Memorial Park and Museum in Japan.
He is the most senior US administration official to ever visit the city or the site, which commemorates those who died in the world's fist atomic bombing.
Mr Kerry is in Hiroshima for the G7 foreign ministers meeting.
US media reports cite government officials saying President Barack Obama is also considering a visit.
Mr Obama will be in Japan for a Group of Seven (G7) meeting of leaders in May. If he goes to Hiroshima, it would be the first time a sitting US president has visited the city.
What happened in Hiroshima?
At 8:10 local time on 6 August 1945 a US B-29 bomber, the Enola Gay, dropped a uranium bomb, nicknamed "Little Boy", which exploded nearly 600m (1,800ft) above the city,
It claimed the lives of at least 140,000 people in the city, about 70,000 of them on the first day. Many more succumbed to injuries and sickness caused by the effects of radiation in the days, months and years that followed.
The bombing - and a second one on Nagasaki three days later - is credited with bringing an early end to World War Two.
Why is Mr Kerry's visit significant?
Japan - the only country to ever be bombed with a nuclear weapon - mourns the terrible human cost of the bombing, which killed and injured a vast number of civilians.
But some in the US and other countries take the view that the nuclear attacks on Hiroshima and Nagasaki ended the war, and so were justified. In 1991, President George Bush famously said that issuing an apology for Hiroshima would be "rank revisionism" and he would never do it.
It was not until 65 years after the bombing that a US ambassador even attended Hiroshima's annual memorial service.
John Kerry's visit comes amid efforts to strengthen the relationship between the two governments, concerned about China's increasing assertiveness in territorial disputes in Asia, affecting Japan and other US allies.
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Has the US ever apologised?No, and it has been made clear by US officials that there will be no apology this time either by Mr Kerry.
"My visit to Hiroshima has a very special meaning about the strength of our relationship and the journey we have travelled together since the difficult time of the war," the US secretary of state told Japanese Foreign Minister Fumio Kishida, who is from the city and represents it in parliament.
The visit, he added, "is not about the past, it's about the present and the future".
Image captionThe Peace Memorial Park draws many visitors, Japanese and foreign, every yearSo why go now?John Kerry is in Hiroshima for the G7 foreign ministers' meetings, which precede a full G7 leaders' gathering in Japan in May.
The ministers, from the UK, Canada, France, Germany, Italy, Japan and the EU, together toured the atomic bomb museum and laid flowers at the cenotaph commemorating its victims.
The US secretary of state will use the visit to promote President Barack Obama's vision of a nuclear-free world - one of the reasons Mr Obama was awarded the Nobel Peace Prize in 2009.
White House officials have reportedly told US media outlets that the visit could inform a decision about whether the president himself will attend the site when he is in Japan for the full G7 meeting in May.
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