The site of the world's worst atomic bomb attack echoed with the choirs of schoolchildren and the solemn ringing of bells Friday as Hiroshima marked its biggest memorial yet and the first to be attended by the U.S. and other major nuclear powers.

Washington's decision to send U.S. Ambassador John Roos to the 65th anniversary of the bombing was seen by many as potentially paving the way for President Barack Obama to visit Hiroshima — which would be unprecedented for a sitting U.S. leader.