In a joint statement after talks between their foreign ministers and defense chiefs, the allies also called on China to be more open about a military buildup that has drawn growing concern here.

The focus of the meeting of US Secretary of State Condoleezza Rice, Defense Secretary Donald Rumsfeld, Japanese Foreign Minister Taro Aso and defense chief Fukushiro Nukaga was an agreement on realignment of US forces in Japan.

But the two sides, meeting at the State Department, also vowed to work together to counter "new and emerging threats" in the world, including Tehran's suspected efforts to develop nuclear weapons.

"They committed to work closely on efforts to convince Iran to suspend all enrichment-related activities and cooperate fully with the International Atomic Energy Agency's investigation, and agreed on the need for concerted United Nations Security Council action," the statement said.

It was issued as the United States was pressing for UN sanctions against Iran but running into resistance from Russia and China, which both hold a veto on the 15-member Security Council.

The Japanese and US delegations renewed their appeal to Pyongyang to return to six-nation negotiations on its nuclear arms program that have bogged down since a declaration of principles was adopted last September.

Their statement "urged North Korea to return expeditiously to the talks without preconditions, to dismantle its nuclear programs in a complete, verifiable and irreversible manner, and to cease all illicit and proliferation activities."

Aso also reiterated that for Tokyo it was "indispensable" to resolve the problem of North Korea's abductions of Japanese civilians in the 1970s and early 1980s for conversion into spies.

China's growing military might was clearly on the minds of the world's superpower and its chief Asian ally, which called for "greater transparency on the modernization of military capabilities in the region."

The joint statement did not mention Beijing by name, but Nukaga was more direct in his own remarks. "Concerning China, along with the economic growth, we see the increase in their defense budget," he said.

"It is very important to work with them so that they will increase the transparency of military capabilities of China to ensure a sense of security among the neighbors," Nukaga said. "And I made this point during the meeting."

The ministers also adopted a roadmap for restructuring American military presence in Japan, which they said "will lead to a new phase in alliance cooperation and strengthened alliance capabilities" in the Asia-Pacific region.

The roadmap would set the pace for the relocation of a key US air base as well as troops from the southern Japanese island of Okinawa by 2014.

Japan is the top US ally in Asia and the two sides have since 2002 been negotiating details of the realignment, including giving Japan's military greater responsibility for security in the region.

The package, originally due to be finalised by the end of March, has been delayed by a dispute over sharing the cost of moving 8,000 US Marines from Okinawa to the US Pacific island of Guam.

Tokyo finally agreed to shoulder 59 percent of the 10.27 billion dollars for the relocation of the Marines and their 9,000 family members. Washington had initially demanded it pay 75 percent of the tab, which includes construction of housing.

The US troop changes are part of a sweeping reorganisation of US forces throughout East Asia. US military presence in Japan and on Okinawa began at the end of World War II.

The two countries recently resolved another sticking point by agreeing to move a sprawling US Marine Corps air base from an urban area in Okinawa to a beach on the island.

There are currently more than 40,000 US troops in Japan, more than half of them in the Okinawa chain where islanders have long demanded a reduction in the US presence.

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