HIROSHIMA, Japan: Japan said it would stand by a self-imposed ban on nuclear weapons as it commemorated the anniversary on Thursday of the world's first atomic attack on the western city of Hiroshima.

Japanese Prime Minister Taro Aso (C) visits the Hiroshima Peace Memorial Museum in Hiroshima, western Japan August 6, 2009, on the 64th anniversary of the world's first atomic bombing on the city. [Agencies]

"I promise again that Japan will continue to adhere to its three non-nuclear principles and take the lead within the international community to abolish nuclear weapons and bring about lasting peace," Aso told a memorial service attended by elderly survivors, children and dignitaries.

Japan often refers to its position as the only country to suffer nuclear attacks when calling for the abolition of atomic weapons. The United States dropped a second atomic bomb on the southern city of Nagasaki days after the one on Hiroshima.

Tokyo does, however, benefit from the shelter of a "nuclear umbrella" extended by its biggest ally, Washington, and many in Japan would be reluctant to see the United States' nuclear deterrent significantly weakened while regional threats remain.

A former Japanese government official recently revealed in media interviews that Tokyo had secretly agreed with Washington in 1960 that Japan would allow stopovers by US military aircraft or vessels carrying nuclear weapons. Japan has repeatedly denied having made such a deal.