Obama will on Friday become the first sitting US president to tour the site of the world's first nuclear bombing. His planned Hiroshima visit has become a focus for discussion worldwide.

Japanese Foreign Minister Fumio Kishida said the US atomic bombings did not conform to humanitarian standards and caused immense loss of life. However, Obama said he would not apologise for the bombing during his visit.

"Because I think that it's important to recognise that in the midst of war, leaders make all kinds of decisions. It's the job of historians to ask questions and examine them," Obama said.

During World War Two, the US launched two atomic strikes on Japan's Hiroshima and Nagasaki. More than 210-thousand people were killed in the bombings. Japan surrendered within days, on August 15th, 1945.

A Pew Research Centre poll found over a half of Americans believe the nuclear strikes were justified. Critics argue that by not apologizing, Obama will allow Japan to maintain its stance as a victim.