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.

Cohen expressed appreciation for Japan's recent moves to strengthen the bilateral partnership, including the implementation of new defense guidelines and joint research into theater missile defense.

"Our alliance has never been so critical and our cooperation has never been so close," he said.

Protesters gather

Thousands of protesters gathered Friday evening at Hibiya Park in Tokyo's Chiyoda Ward to denounce the planned construction of a new facility in Nago, Okinawa Prefecture to take over functions of Futenma Air Station.

Citizens' groups organizing the rally said the construction plan tramples down the opinions of Nago citizens that they want no more military base, and also destroy the precious natural environment in the region.

Takuma Higashionno from the Henoko district of Nago, chosen in December as the location for the new base, told participants that the military base issue represents the structure of Japanese society, where something unwelcome is always imposed upon the the weak.

"What is happening in Okinawa is an epitome of Japanese society," he said.

The Henoko district is known as a habitat for the endangered dugon. Members of environmental groups also took part in the rally to oppose the base plan.

Takako Doi, leader of the Social Democratic Party and Tetsuzo Fuwa, chairman of the Japanese Communist Party, also attended the gathering.

Organizers said about 4,000 people took part in the rally, who later staged a demonstration march in Ginza.

U.S. hails Atsugi action

WASHINGTON (Kyodo) The Pentagon said Thursday that it welcomes Japan's steps to resolve an air pollution problem in Kanagawa Prefecture that has affected U.S. military personnel and their families at the Atsugi Naval Air Facility.

Pentagon spokesman P.J. Crowley told a news briefing, "We are very pleased with the action that the Japanese government is taking in concert with our base on that issue.

"We're gratified that at the national level there now is the commitment and support and the joint effort that we think will correct this problem," Crowley said.

During talks between U.S. Defense Secretary William Cohen and Defense Agency chief Tsutomu Kawara, Japan promised that the government is ready to provide alternative housing for the pollution-affected military personnel.

The U.S. has been complaining that the health of its personnel and their families is affected by dioxin released from incinerators belonging to the private Japanese company Enviro-Tech, also known as Shinkanpo, which is located adjacent to the joint-use air base.