Hiroshima mayor rejects nuclear deterrence claims by world's nuclear powers as "folly" as Japan marks the 78th anniversary of the US atomic bombing on the city, massacring nearly 100,000 people with no apologies.

Russia's former president Dmitry Medvedev says Japanese Prime Minister Fumio Kishida has betrayed the rights of hundreds of thousands of victims of US nuclear bombings of Hiroshima and Nagasaki.