Tokyo, Japan (CNN) -- China's military puts the scare into Japan, and the U.S. is a key to keeping peace in the region, Japan's Defense Ministry said in a white paper Friday.
"The lack of transparency in [Chinese] national defense policies and the direction of military power are a concern for the region and the international community, including our country, and we need to carefully analyze it," the 488-page Defense of Japan 2010 report says, according to Japan's Kyodo news agency.
The annual report cites worrisome moves by China's military, including 10 Chinese submarines and destroyers being spotted west of Japan's Okinotori Island in April 2010 and a Chinese nuclear submarine entering Japanese waters in November 2004.
Conflicting claims to territorial waters and islands -- and the natural resources that go with them -- are one of the Asia-Pacific region's flashpoints. China disputes most of its neighbors' claims and claims nearly the entire South China Sea as its own.
Japan and China are currently involved in a conflict over a Chinese trawler that collided with Japanese patrol ships Tuesday off the disputed Diaoyu Islands, in the East China Sea.
The Japanese coast guard arrested the trawler's captain, alleging that he obstructed public officers while they performed their duties.
"China will never accept the Japanese side's applying domestic law to the Chinese fishing boat operating in that area," said Chinese Foreign Ministry spokeswoman Jiang Yu, according to state-run media.
Japan's handling was "absurd, illegal and invalid," he said, reported the Xinhua news agency.
The Japanese defense white paper also focused on the role of the U.S. military in protecting Japan from possible attack. In that role, the U.S. military is best positioned on the Japanese island of Okinawa, the report indicated.
The location of the U.S. military in Okinawa has strained relations between the two allies, however. Many Okinawans want the base moved, in response to various crimes committed by military personnel against Japanese civilians.
The defense report also called North Korea's nuclear and missiles programs an "extremely destabilizing factor" in the region. The North's moves pose "grave dangers," the white paper said.
In May 2009, North Korea detonated a nuclear device. The international community condemned the test, and the U.N. Security Council stepped up economic sanctions against the North.
China remains North Korea's key ally and biggest trading partner, providing the starving nation with food, as well as weapons.