TOKYO - Japan's government on Tuesday vowed to stick to its ban on nuclear arms after a probe showed its predecessors may have turned a blind eye to breaches, but said ties with security ally Washington would not be affected.

The United States had urged Japan not to let the investigation into past secret pacts over nuclear weapons damage their relationship, which has been shaken by a feud over the relocation of a U.S. Marine base on the island of Okinawa.

This should not affect U.S.-Japan relations, at the same time, there is no need to change the three non-nuclear principles, Prime Minister Yukio Hatoyama told reporters, referring to Japan's policy of not possessing or producing atomic weapons, or allowing them into the country.

A panel of experts commissioned by Foreign Minister Katsuya Okada examined thousands of documents over a period of months, concluding that there was a tacit agreement between Tokyo and Washington that may have allowed U.S. vessels carrying nuclear weapons to enter Japanese ports without prior discussion.

Okada touted the report, which contradicted previous governments' denials, as a victory for democracy months ahead of an upper house election the ruling Democratic Party must win in order to avoid policy deadlock.

Making the facts clear is the very basis of democracy, he told reporters.

The six-month-old government's handling of ties with Washington has weighed on voter support, adding to falls sparked by a series of financial scandals involving ruling party lawmakers.

During a visit to Tokyo in October, U.S. Defence Secretary Robert Gates urged Japanese Defence Minister Toshimi Kitazawa to ensure the investigation of the pacts did not damage the U.S.-Japan relationship.

In calling for a world free of nuclear weapons, Japan often emphasises its status as the only country to have suffered nuclear attacks.
But Tokyo also benefits from the shelter of the U.S. nuclear umbrella, and many in Japan would be reluctant to see the United States' nuclear deterrent significantly weakened in the face of a resurgent China and threats from North Korea.

Okada said he did not envisage the United States bringing nuclear weapons to Japan after a 1991 change in policy by then U.S. President George H.W. Bush saw them removed from ships. He did not specify how Japan would deal with any threat of nuclear attack in the future.

(Additional reporting by Linda Sieg; Editing by Jerry Norton)

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