Washington: The US government has declassified the fact it held nuclear weapons on Okinawa in Japan during the Cold War, though the matter had long been an open secret.

A Department of Defence website states the Pentagon has declassified “the fact that US nuclear weapons were deployed on Okinawa before Okinawa’s reversion to Japan on May 15, 1972”.

The National Security Archive at George Washington University welcomed the disclosure, but pointed to US Air Force photos depicting nuclear weapons on the island that have been publicly available for more than 25 years.

“However welcome the release may be, its significance is somewhat tempered by (that) astonishing fact,” the non-governmental research group said in a statement Friday.

The group added that the US government had wasted an “inordinate” amount of time and resources by delaying the declassification.

Japan is the only nation to have been attacked with nuclear weapons. The United States dropped atom bombs on Hiroshima and Nagasaki in 1945, killing more than 210,000 people and leading to Japan’s surrender in World War II.

Japan has since campaigned to abolish the weapons. Former prime minister Eisaku Sato won the Nobel Peace Prize largely for his “three principles” — that Japan will not possess, produce or allow nuclear weapons on its soil.

Okinawa remained under US control until 1972, and many parts of the archipelago are still used for US bases.