I have written about this problem in the past articles on my blog. And, here. Yesterday, I came across with an article in Ashahi that tells some developments on the issue. I have translated it into English.
The US State Department spokesman PJ Crowley announced Wednesday that John Ross, the ambassador to Japan will take part in the annual peace memorial ceremony August 6 in Hiroshima. He says that the purpose of Ross's participation to it is to express the honor for all victims of the World War Ⅱ. But, in another development on this issue, a high level official in the department said clearly that the USA does not have any idea that it will express apology to Japan about using the mass destruction weapons in WW2 in the ceremony.