The US-China ties will be "complex" as there remain areas of concern including in the disputed South China Sea, Defence Secretary Ashton Carter said as he underlined American military's presence in the region and its role in upholding the rules-based navigation system.
"It is clear that the US-China relationship will be complex as we continue to balance our competition and cooperation," Carter told the Senate Armed Services Committee.
He said there are opportunities to improve understanding and reduce risks with China. "We've agreed to four confidence- building agreements, including one meant to prevent dangerous air-to-air encounters. But there remain areas of concern."
The top Pentagon official said the US and virtually all nations in the region were deeply concerned about the pace and scope of land-reclamation in the South China Sea, the prospect of further militarisation, as well as the potential for these to increase the risk of conflict among claimant states.
China claims most of the South China Sea, but Vietnam, the Philippines, Malaysia, Brunei and Taiwan have rival claims.
The US has decades-old military presence in the region and it has been been instrumental in upholding the rules-based international system and laid the foundation for peace and security in the region, Carter said about the sea lane through which more than USD5 trillion in global trade passes annually.
"Our interest is in maintaining freedom of navigation and overflight, full and unimpeded lawful commerce, and that disputes are resolved peacefully," Carter said.
He said the US also expects China to uphold President Xi Jinping's pledge not to pursue militarisation in the Spratly Islands. "We are closely watching the long-term, comprehensive military modernisation program that China, as well as other countries, continues to pursue."
While there is no question that the US retains a decisive military edge in the Asia-Pacific, China is investing in capabilities to counter third-party -- including the US -- intervention during a crisis or conflict, he said.
These capabilities include ballistic and cruise missiles of increasingly greater range and accuracy, counter-space and offensive cyber capabilities, and electronic warfare systems.
Testifying at the same committee, Gen Joseph F Dunford, chairman of the Joint Chiefs of Staff, said China's expanding presence in Asia increase the "possibility of miscalculation."
"China is also seeking to improve the joint capability of its armed forces to project power -- enhancing its ability to fight and win a high-intensity regional conflict," he said.
"China is also investing in land attack and anti-ship cruise missiles, counter-space weapons, cyber, improved capabilities in nuclear deterrence and long-range conventional strike, advanced fighter aircraft, integrated air defences, undersea warfare, and command and control capabilities."
Dunford said China's use of computer network attacks in a conflict with the US could seriously limit access to cyberspace and degrade deployment and sustainment of forces.
"By pursuing a diverse and capable range of offensive space control and counter-space capabilities, China is also working to diminish US space dominance," he said.
