Japan confirmed for the first time Tuesday the existence of once-secret Cold War-era pacts with the U.S. that tacitly allowed nuclear-armed warships to enter Japanese ports in violation of Tokyo's postwar principles.

While declassified U.S. documents have already confirmed such 1960s agreements, Tuesday's revelation broke with decades of official denials.

The investigation by a government-mandated panel is part of Prime Minister Yukio Hatoyama's campaign to rein in the power of bureaucrats and make his government, which was elected to power last year, more open than that of the long-ruling conservatives, who repeatedly denied the existence of such pacts.

"It's regrettable that such facts were not disclosed to the public for such a long time, even after the end of the Cold War era," Foreign Minister Katsuya Okada told a news conference, adding that the investigation was meant to restore public trust in Japan's diplomacy....