Finance Minister Naoto Kan said Friday he believes the Japanese government paid more than a total of $320 million for costs related to the 1972 reversion of Okinawa under "a secret pact in a broad sense" with the United States.

But Kan said the Finance Ministry could not find sufficient evidence to establish that Japan's zero-interest account at a U.S. Federal Reserve Bank was used to raise extra money for Washington.

The Japanese government made a deposit of about $53 million into the bank account in 1972 and it was kept through 1999, according to the ministry.

The ministry's probe into the purported clandestine deals related to the reversion of Okinawa to Japanese sovereignty from U.S. control was commissioned by Kan and his predecessor Hirohisa Fujii, both lawmakers of the Democratic Party of Japan, which last summer ended more than half a century of nearly unbroken rule by the Liberal Democratic Party.

The investigation was launched in parallel with the Foreign Ministry's probe into whether there were secret pacts during the Cold War between Tokyo and Washington, including one that allows U.S. nuclear-armed vessels to visit Japanese ports.

Declassified documents in the United States and testimonies of former Japanese government officials confirmed the existence of some secret pacts in the 1960s and 1970s. But previous Japanese governments have successively denied their existence.

Kan's announcement came after a Foreign Ministry panel of experts concluded Tuesday that some of the most important bilateral agreements of the period were reached in backroom deals.

Among others, the panel said a secret pact can be confirmed in which Japan consented to shoulder $4 million in costs on behalf of Washington to restore Okinawa land plots, which had been used by U.S. forces, to their original state.

But the issues related to the bank account were not subject to the examinations of the Foreign Ministry panel.

Japan's official stance has been that the government in power at that time paid a total of $320 million for costs related to the reversion, while some experts on Japan-U.S. relations have claimed that the actual costs were as much as $685 million, citing some records in the declassified documents in the United States.

One declassified memorandum of understanding that Japan's former top financial diplomat Yusuke Kashiwagi negotiated in 1969 with his U.S. counterpart, Anthony Jurich, indicates that Japan had promised to pay more than $320 million.

The memorandum signed by the two negotiators touches on how to deal with Japan's new dollar holdings that would result from converting Okinawa dollars into yen with the 1972 reversion.

The memo, dated Dec. 2, 1969, said, "The Bank of Japan will deposit $60 million or the amount of currency actually converted, whichever is greater, in a non-interest bearing account with the Federal Reserve Bank of New York acting as principal and agent of the U.S. Treasury."

Then it said, "Funds shall remain on deposit for at least 25 years."

If Japan did not let the dollar funds sit in the interest-free account, it would have been able to earn interest on the deposit.

Some experts, including Masaaki Gabe, a University of Ryukyus professor, who obtained a copy of the memo from the U.S. National Archives, believe that Japan used the account to effectively increase its payment to the United States for the return of Okinawa.

The negotiators who represented the Finance Ministry in the course of realizing the reversion of the southern island and former Finance Ministers Takeo Fukuda and Kashiwagi are no longer alive.