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.

Kan made the remarks after releasing the results of the Finance Ministry's months of investigation into Japan's zero-interest account at a U.S. Federal Reserve Bank in connection with the reversion of Okinawa to Japanese sovereignty from U.S. control.

The main subject of the investigation was one declassified memorandum of understanding that Japan's former top financial diplomat Yusuke Kashiwagi negotiated in 1969 with his U.S. counterpart, Anthony Jurich, which indicates that Japan had promised to pay more than $320 million for the reversion.

"Between Japan and the United States at that time, I believe there were secret promises regarding the burden going beyond $320 million, which has been stipulated in the agreement on the return of Okinawa, and how other money (for the reversion) should be spent," Kan said at a news conference at the ministry.

He said the memorandum probably served as "the starting point" for negotiations between the two countries toward reaching clandestine deals.

"I have summed up that the document functioned as a secret pact in a broad sense," Kan said.

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.

Combined with the Bank of Japan's deposit of around $50 million, Japan put about $103 million into the account, which is equivalent to the amount of new dollars that the government obtained from converting Okinawa dollars into yen with the 1972 reversion.

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

The ministry's probe into the purported clandestine deals related to the reversion 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 have 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 Tokyo 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.

The memorandum signed by Kashiwagi and Jurich touches on how to deal with Japan's new dollar holdings.

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."

It also 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 Minister Takeo Fukuda and Kashiwagi are no longer alive.