U.S. Defense Secretary William Cohen on Friday rejected the 15-year time limit proposed by the mayor of Nago, Okinawa Prefecture, for a new heliport to relocate the helicopter operations at Futenma Air Station.

"Security needs are always determined by circumstances, not by any artificial limitations," Cohen told the Japan National Press Club in Tokyo before leaving for South Korea later in the day.

"I would assume the Japanese people would also support such a policy, that we define the relationship by the nature of the threat that exists," he added.