China on Tuesday accused the US of hyping up the Chinese military threat after the Pentagon asserted in its annual Chinese military assessment that Beijing was involved in cyber espionage against Washington and alleged China's "growing assertiveness" on maritime territorial claims.

The military reports made "irresponsible comments about China's legitimate and normal defense-building and hyping up the so-called idea of a China military threat," Chinese foreign ministry spokeswoman Hua Chunying told reporters in Beijing.

"This behavior is not conducive to mutual trust or cooperation," she said. "We express firm opposition to this and have made representations to the US."

"China is committed to a path of peaceful development and pursues a defensive defense policy," she added, saying that "we resolutely oppose any form of hacking attacks."

The US Department of Defense (DOD) on Monday released a report on China's military development, in which it for the first time cited the Chinese government as responsible for cyber attacks targeting the US government and businesses.

"China is using its computer network exploitation (CNE) capability to support intelligence collection against the US diplomatic, economic, and defense industrial base sectors that support US national defense programs," the report said.

"In 2012, numerous computer systems around the world, including those owned by the US government, continued to be targeted for intrusions, some of which appear to be attributable directly to the Chinese government and military," it asserted.

The DOD alleged that such "cyber espionage" could finally benefit China's arms development and military programs.

The Pentagon's accusations of China's "cyber espionage" were obviously well choreographed in accordance with earlier hyping-up tactics, said Li Li, a professor with the Beijing-based PLA National Defense University. She cited a series of reports this year by US cyber-security firms that listed China as an origin of cyber attacks targeting the US.

"The previous accusations against China can be seen as a prelude to the Pentagon report, which came as no surprise," Li told the Global Times, noting that by doing so, Washington wanted to create an atmosphere to boost its control over cyber space.

According to a report in February by China's National Computer Network Emergency Response Technical Team, China's cyber security has come under increasingly severe threats, with the US being the largest source of cyber attacks.

The Pentagon also claimed in the report that China's act of drawing straight baseline claims around the Diaoyu Islands is inconsistent with international law, despite Washington's repeated statement that it is not taking sides in the islands disputes between China and other countries.

"In this report, we do highlight China's increased assertiveness with respect to its maritime territorial claims," David Helvey, US Deputy Assistant Secretary of Defense for East Asia told reporters at the Pentagon.

Li Jie, a Chinese Navy military expert, told the Global Times that by mentioning the Diaoyu Islands dispute in the report, Washington sent a signal that it would strengthen its military alliance with Japan in an joint effort to contain China.

"For the US, tightening the control of Diaoyu would be a step toward further blocking China in the first island chain," Li Jie said.

The report also criticized China for its "lack of transparency" in defense spending.

China announced a budget of $114 billion in its annual defense spending in March, the report said, but alleged that China's real military spending in 2012 was between $135 and $215 billion.

"What concerns me is the extent to which China's military modernization occurs in the absence of the type of openness and transparency that others are certainly asking of China," Helvey told reporters.

However, China has issued eight white papers on national defense since 1998 to enhance its military's transparency. The latest one in April saw Beijing reaffirm the defensive nature of its national defense policy and made it clear that its armed forces staunchly uphold world peace and regional stability.

Agencies contributed to this story