This is the first time US and other nuclear powers attended the memorial for 1945 nuclear attack on Japan. The United States' decision to send Ambassador John Roos to the memorial is the first step towards US President, Barack Obama's visit to the country, said international media reports.
"For the sake of future generations, we must continue to work together to realise a world without nuclear weapons," the US ambassador said in a statement.
UN Secretary-General Ban Ki-moon was also one among the top officials who attended the 65th memorial. A total of 74 nations were represented.
"Life is short, but memory is long. For many of you, that day endures ... as vivid as the white light that seared the sky, as dark as the black rains that followed," said Mr Ban, expressing hope that the 2010 memorial will send a strong signal to the world that nuclear weapons must be destroyed.
However, China, which sent a low ranking official in 2008, chose not to participate this year. The reasons behind this decision is unknown.