NEW YORK (AP) — President Barack Obama on Thursday called the U.S.-Japan alliance a cornerstone of world peace and security, as senior U.S. defense officials backed Japan, a top U.S. ally, in a tense territorial dispute with China.

With Japanese Prime Minister Naoto Kan at his side ahead of private talks on the sidelines of a United Nations global summit, Obama didn't publicly mention the heated diplomatic clash over Japan's arrest of a Chinese fishing boat captain near islands both Japan and China claim as their own.

But he made clear that the U.S.-Japan alliance is crucial to stability in Asia and to both U.S. and Japanese security.

"We believe it is one of the cornerstones of peace and security throughout the world," Obama said.

Beijing is furious over the arrest of the Chinese captain whose fishing boat collided two weeks ago with Japanese coast guard vessels. Japan extended the detention of the captain Sunday. China quickly suspended high-level contacts with Japan and announced that Premier Wen Jiabao wouldn't be meeting with Kan during this week's U.N. meetings.

In Washington, the top U.S. military officer said the United States is backing Japan.

Chairman of the Joint Chiefs of Staff Adm. Mike Mullen told reporters that the United States hoped that diplomatic efforts would ease tensions soon. But, he added, "obviously, we're very, very strongly in support of ... our ally in that region, Japan."

Defense Secretary Robert Gates, also commenting on the incident, said: "We would fulfill our alliance responsibilities." He didn't elaborate.

The U.S. State Department urged China and Japan to aggressively and quickly resolve the matter.

Spokesman P.J. Crowley told reporters that Secretary of State Hillary Clinton told new Japanese Foreign Minister Seiji Maehara in a meeting Thursday that good ties between China and Japan are crucial to Asia's prosperity.

"Neither side wants to see the situation escalate to the point where it has long-term regional impact," Crowley said.

The White House said the United States wouldn't be mediating the dispute.

"These two countries have a history with each other and nationalist sentiments in both countries that can be stirred up, should the problem stagnate," Jeffrey Bader, an Asia expert on Obama's National Security Council, told reporters. "So we do want to see calm and restraint on both sides."

He said the issue didn't come up in talks between Obama and Chinese Premier Wen Jiabao.

Kan, in his public comments ahead of the Obama meeting, talked of his new Cabinet, which he announced last week after winning a divisive Democratic Party leadership election.

Kan, a fiscal disciplinarian who took office just three months ago, has promised to push ahead with efforts to cap spending, create jobs and build party unity.

Japan has struggled to maintain steady leadership, with five prime ministers in the past four years.

The United States and Japan are strong allies, with 47,000 U.S. troops stationed in Japan, but ties have been strained over the relocation of a U.S. Marine base on the island of Okinawa. People in Okinawa, which hosts three-quarters of all U.S. military facilities in Japan, have pushed for U.S. bases to be moved off the island.

Under a 2006 agreement to reorganize U.S. troops in Japan, Washington is to move 8,000 Marines from Okinawa to the U.S. territory of Guam and relocate U.S. Marine Air Station Futenma to a less crowded part of the island by 2014.


AP writers Desmond Butler and Anne Flaherty in Washington contributed to this report.