The annual US report on China's military capabilities often produces sensational headlines, but a Pentagon official on Monday tried to draw attention to the evolving relationship between the two countries' armed forces.

"Over the course of 2012, the armed forces of the United States and China made progress in building positive momentum in their defense contacts and exchanges," David Helvey, deputy assistant secretary of defense for East Asia, told a press briefing on the 2013 report on military and security developments in China. The yearly report to Congress has been required by law since 2000.

Helvey emphasized US efforts toward a healthy, stable, reliable and ongoing military-to-military relationship with China, a tone set by President Barack Obama and then-president Hu Jintao of China in early 2011.

He described the bilateral military ties as an important component of US-China relations overall.

"Indeed, having this type of relationship is an important part of our large strategy to rebalance to the Asia-Pacific region," Helvey said.

He highlighted senior-level visits from 2012: Defense Minister Liang Guanglie to the US in May; the head of US Pacific Command, Navy Admiral Samuel Locklear, to China in June; Army Deputy Chief of the General Staff Cai Yingting to the US in August; and Defense Secretary Leon Panetta to China in September.

Also stressed was US participation in a number of bilateral talks, such as the countries' security and strategic dialogue, annual defense consultative talks and defense coordination.

The Pentagon's 83-page report also provides a long list of bilateral contacts and exchanges over the past year as well as plans for 2013.

Describing the exchanges as "playing a role of enhancing mutual understanding and improving communications between the two militaries", Helvey said the US and China also explored concrete, practical ways to cooperate.

These include their first-ever counterpiracy exercise in September, followed by a US invitation to China to take part in the Rim of the Pacific drills, the largest naval exercise in the world. China has said it will participate.

"We will continue to use military engagement with China as one of the several means to expand the areas where we can cooperate, discuss frankly our differences and demonstrate the US commitment to the security of the Asia-Pacific region," Helvey said.

China has made great progress toward transparency in defense and security affairs, but he also cautioned: "Despite the information available and China's regular white paper on defense, many uncertainties remain, which only underscore the importance of building a military dialogue with China that is sustained and substantive."

Among those uncertainties, he said, the "greatest concern" comes from a lack of openness and transparency as to the extent of China's military modernization.

The report said China continues to pursue a long-term, comprehensive military modernization program designed to improve the capacity of its armed forces to fight and win short-duration, high-intensity regional military conflict.

It alleges that preparing for potential conflict in the Taiwan Straits appears to remain the principal focus and primary driver of China's military investment.

Helvey pointed to China's increased assertiveness with respect to its maritime territorial claims but reiterated that the US doesn't take a position as to sovereignty assertions but encourages all parties to address issues peacefully, through diplomatic channels and in a manner consistent with international law.

"The report provides a lot of information. I think the report also poses a number of questions - questions for which we don't have answers," he said.

While it focuses on China's strategy, military modernization, Taiwan contingencies and military exchanges, the report also mentions China's first aircraft carrier, stealth aircraft, space-based imaging and remote sensing as well as integrated air defense.

The report said that as the US builds a stronger foundation for a military-to-military relationship with China, it also will continue to monitor China's evolving military strategy, doctrine, and force development and encourage China to be more transparent about its military modernization program.

"With new direction from the top, the bilateral military relationship is on a healthy trajectory after more than a decade of changing and contradictory interactions," said Douglas Paal, a China specialist and vice-president for studies at the Carnegie Endowment for International Peace in Washington. "The outlook is for a deepening and enduring mil-mil relationship, but one that starts from a very low base, with much room for improvement."

Zhiqun Zhu, a professor of political science and international relations at Pennsylvania's Bucknell University, said the report reflects America's mixed feelings about the growing power of China.

"On the one hand, it reaffirms the US government commitment to building strong, positive and sustainable bilateral relations, including military-to-military relations. On the other hand, it also shows America's concerns about the speed and scale of China's military modernization," he said.

Bonnie Glaser, a China specialist at the Center for Strategic and International Studies, said both countries have recognized that bilateral military ties must be strengthened if the US and China are to have a stable and positive relationship overall.