Tokyo: A secret agreement under which Japan allowed the US military to bring nuclear weapons to the Asian nation has been uncovered despite years of denial of its existence by Tokyo, media reports said Tuesday.

The 1969 contract, signed by then US President Richard Nixon and Japanese Prime Minister Eisaku Sato, was kept by the Sato family, said the Yomiuri Shimbun newspaper, which showed a picture of the two-page document.

The existence of the agreement has been denied for decades by past conservative administrations, which issued a complete ban on nuclear weapons, including transporting of such items by its main ally, the United States.

The discovery was a major step forward for the Democratic Party of Japan, which formed a centre-left government in September, ousting the conservative Liberal Democratic Party.

Foreign Minister Katsuya Okada has set up a committee of experts to examine allegations about various hidden agreements between previous regimes and Washington.

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.