TOKYO (AFP) - Japans opposition has pledged to raise with Washington an alleged Cold War-era pact allowing US nuclear-armed ships to visit Japan, it was reported Thursday. Japan adopted a three non-nuclear principles policy of not possessing or producing nuclear weapons or allowing them on its territory in 1968, and it regularly speaks out in favour of a nuclear-weapons-free world. Tokyo and Washington will thoroughly discuss the issue if we take the reins of government, Yukio Hatoyama, the leader of the main opposition Democratic Party of Japan (DPJ), was quoted by the Japan Times as saying. It is most desirable to openly abide by the three non-nuclear principles, added Hatoyama, whose party is hoping to clinch power in a general election next month. The issue is sensitive in Japan, the only country to have suffered nuclear attacks when bombed by the United States towards the end of World War II. The Mainichi Shimbun daily reported last month that a pact allowing visits by nuclear-armed US ships existed, quoting Ryohei Murata, a former vice foreign minister who served in the late 1980s. It said the accord was reached when Japan and the United States revised their security treaty in 1960 to give a more equal footing to Japan, which was rebuilding itself from the devastation of World War II. Japans government has always denied there was such a pact. In 1991 US president George H.W. Bush announced that US vessels would no longer carry tactical nuclear weapons, rendering any such pact with Japan obsolete. A ruling party lawmaker, Taro Kono, told AFP he believes it existed, noting that official US documents and former US ambassador to Japan Edwin O. Reischauer had referred to the agreement. It is only the Japanese government that is still denying it, he said. We need some kind of nuclear strategy against North Korea. As long as the Japanese government lies to the people, it is very difficult to debate, said Kono, chairman of the lower house foreign affairs committee. Voter surveys suggest the DPJ is likely to win the general election which Aso has called for August 30 ending more than half a century of almost unbroken rule by the LDP.