A fresh drive to declare nuclear weapons illegal is gathering international momentum ahead of a historic visit by Barack Obama to the Japanese city of Hiroshima on Friday.

But Australia stands as a key part of the "weasel group" of countries opposed to banning the bomb - a stance Indonesia's former foreign minister has warned undermines the chances for nuclear disarmament.

Mr Obama's visit to Hiroshima will be the first for a serving US President. The city was the first to suffer nuclear attack, after the US dropped an atomic bomb in the last days of World War II, killing more than 140,000 people.

Mr Obama has ruled out any official apology for the Hiroshima bombing, but anti-nuclear campaigners and Japanese survivors from the 1945 bombing hope his visit will draw attention to the catastrophic human cost of atomic weapons.