A Japanese government team has found documents on an alleged secret pact with the United States to transport nuclear weapons through its territory, after decades of official denial, reports said on Sunday.
Prime Minister Yukio Hatoyama's centre-left government launched a probe into the alleged nuclear pact and other secret agreements with the United States days after it took office in September.
The probe team reported to Foreign Minister Katsuya Okada on Friday that it had discovered documents linked to the pact from among thousands of files at the foreign ministry, the Mainichi Shimbun and Yomiuri Shimbun newspapers reported, citing unnamed ministry sources.
"Foreign minister admits 'nuclear secret pact'" declared the headline in the Mainichi Shimbun, while the Yomiuri Shimbun echoed: "Government view likely to change -- 'nuclear secret pact'."
The existence of the agreement has been denied for decades by previous conservative administrations, even though US documents declassified last month showed US officials believed they had an understanding with Japan when the allies signed a new security treaty in 1960.
"The question of black or white will become clear in January. We will clear the burden of previous administrations which had insisted there was no secret pact," Okada said Saturday, the newspapers reported.
Okada will set up a committee of experts to examine the documents before announcing the government's final judgement in January whether the secret pact did indeed exist, they said.
Japan, the only nation to have suffered nuclear attacks and which has campaigned for the worldwide abolition of the ultra-destructive weapons, has had a policy of not possessing, producing or allowing nuclear weapons on its territory since 1967.
The probe team is believed to have found documents related to the records of discussions in 1960 when Japan and the United States signed a new security treaty, the newspaper reports said.
A confidential US State Department memo prepared in 1960 for then secretary of state Christian Herter said Washington had to consult Japan on the "introduction of nuclear weapons."
But it said that the United States, which has stationed troops in Japan since its defeat in World War II, could use Japanese soil "as needed" in an emergency if communist neighbour North Korea launched an attack.
In 1991, then US president George Bush announced that US vessels would no longer carry tactical atomic arms, rendering any pact with Japan allowing US nuclear-armed ships to visit obsolete.
The Japanese team is also probing other alleged pacts on a contingency plan on the Korean peninsula, allowing nuclear weapons on Japanese soil in the event of an emergency and an agreement for Japan to pay costs linked to returning the southern island of Okinawa to Japan in 1972 after US military occupation.
The United States dropped atom bombs on Hiroshima and Nagasaki in 1945, killing more than 210,000 people and ending World War II.