"There are deep exchanges between the Japanese and the U.S. governments...But I don't think that Tomahawk will be reloaded," Okada told a parliamentary committee, a day after a Foreign Ministry panel acknowledged the existence of a "tacit agreement" that led Japan to allow U.S. nuclear-armed ships to visit Japanese ports without prior consultation.

Okada's remarks suggested that the United States may have explained to Japan about a policy to retire its Tomahawk missiles, which is expected to be included in the "Nuclear Posture Review" Washington plans to announce possibly by the end of this month.

Okada said Tuesday what the panel acknowledged as a secret agreement in a broad sense is no longer effective, because the United States has made clear since 1991, after the end of the Cold War, that it will withdraw all tactical nuclear weapons from its surface ships and attack submarines.

But he also said that he cannot completely rule out the possibility that nuclear weapons had been brought into Japan before 1991, despite Japan's three non-nuclear principles of not possessing, producing or allowing nuclear weapons on its territory.

Okada reiterated that Japan would continue to uphold the principles, first introduced in 1967.