Thousands gathered at the city's peace memorial on August 6 to observe one minute's silence in memory of the 140,000 killed by the US atomic attack in 1945.

Mr Kan used the occasion to address the crisis caused by a tsunami wrecking the Fukushima Daiichi power plant in March.

He promised to challenge "conventional beliefs" that nuclear energy was safe.

The Fukushima plant continues to leak radioactive material, nearly five months after a 9.0 magnitude earthquake triggered the tsunami which caused the damage. It was causing serious concerns not just in Japan but across the world, Mr Kan said.

About 30% of Japan's electricity was nuclear generated before the Fukushima crisis, and the country had previously targeted raising that figure to 53% by 2030.

But Mr Kan said: "I will reduce Japan's reliance on nuclear power, aiming at creating a society that will not rely on atomic power generation."

The prime minister spoke after laying a wreath of yellow flowers at Hiroshima Peace Memorial Park, where doves were released as a symbol of peace.

Japan has long vowed never to make or possess nuclear weapons but had embraced nuclear power as it rebuilt after World War II.