U.S. President Barack Obama says he will soon decide how many additional troops to send to Afghanistan, saying any delay in his decision came because he is determined to "get it right."

In a joint news conference in Tokyo with Japanese Prime Minister Yukio Hatoyama, Mr. Obama rejected recent criticism that his administration has been stalling the decision.  

Obama said U.S. policy on Afghanistan must protect America from terrorist networks, but he added that the U.S. commitment to Afghanistan is not, as he put it, "open-ended."

Obama and Hatoyama pledged to revise the long-standing alliance between their countries after more than an hour of talks at the new Japanese leader's office Friday.

Mr. Hatoyama told reporters he and the U.S. president will collaborate on a range of difficult issues, including climate change, nuclear non-proliferation and Afghanistan.

The prime minister reiterated his government's vow to end the Japanese naval mission to refuel ships deployed to Afghanistan, but said Tokyo would commit $5 billion in aid to Kabul.

In a joint statement released after the summit, both leaders say they will cooperate in clean energy initiatives in order to achieve an 80 percent cut in greenhouse gas emissions by 2050.  

Mr. Obama arrived in Tokyo hours earlier with the aim of improving ties with the longtime U.S. ally.  Mr. Hatoyama led his center-left Democratic Party to victory in August promising a much more independent relationship with Washington.

His campaign pledge to move a U.S. Marine air base off the southern island of Okinawa has rankled the Obama administration.  The pledge would renege on an agreement reached in 2006 that calls for relocating the Futenma base to a more remote part of Okinawa.  Some residents have complained about noise, pollution and base-related crimes.  

Mr. Hatoyama says he will seek to resolve the issue over the base as soon as possible.  

Japan is the first leg of Mr. Obama's eight-day tour of Asia.  He told reporters Friday that he will make it clear to the leaders of the region the future of the United States is "inextricably linked" to the Pacific Rim region.  

Mr. Obama will deliver a major speech in Tokyo Saturday in which he will spell out his vision of U.S.-Asia relations.

From Tokyo, Mr. Obama travels to Singapore for a summit of 21 Asia-Pacific economies.  Mr. Obama will then visit Shanghai and Beijing in China, and Seoul, South Korea.