TOKYO - Japan and the United States reaffirmed their five-decade security alliance on Tuesday, vowing to expand ties into new areas even as they squabble over the relocation of a U.S. Marine base.

They will work with China and also jointly deal with North Korea's nuclear and missile threats, the two countries' foreign and defence ministers said in a statement to mark the 50th anniversary of the U.S.-Japan security treaty.

The Ministers stress that the United States and Japan will work to advance cooperative relations with China, welcoming it to play a constructive and responsible role in the international arena, they said.

The security treaty, obliging Japan to provide land and facilities for military bases and the United States to protect Japan, has been stable, but relations have been strained lately by a feud over a U.S. base in southern Japan and questions about the future of ties as both adapt to a rising China.

We will need to have discussions on what we must do to prevent China from becoming a realistic threat, Japanese Foreign Minister Katsuya Okada told a news conference, adding that China, with its economy growing, was expanding its military.

Japanese Prime Minister Yukio Hatoyama's Democratic Party, which took power in September pledging a diplomatic stance more independent of Washington and closer ties with Asian neighbours, faces a dilemma over the U.S. airbase.

Hatoyama said ahead of his party's landslide election victory that the Futenma airbase in Okinawa should be moved off the island, fanning hopes of local residents.

Washington, however, has insisted Tokyo stick to a 2006 deal to relocate base facilities to a less crowded part of the island.

Hatoyama has promised to decide on the matter by May, although a Jan. 24 mayoral election in Nago City, Okinawa, site of the original relocation spot, would complicate matters if an anti-base candidate wins.

A delay in the decision could hurt Hatoyama's ratings which have suffered from doubts about his leadership ability.
The two sides are just beginning to work on defining a new direction for the alliance, which could include tighter links in intelligence and missile defence but also cooperation in non-security areas such as fighting global warming.

Hatoyama said on Tuesday he wants to have visible results by the end of the year from the talks.

(Reporting by Chisa Fujioka; Editing by Edwina Gibbs)