The Chinese Foreign Ministryas lodged "stern representations" with the United States after US President Barack Obama signed into law a US defense policy bill that suggests a plan to conduct high-level military exchanges with Taiwan.

Part of the $618.7 billion National Defense Authorization Act "expresses the sense of Congress that (the US Department of Defense) should conduct a program of senior military exchanges between the United States and Taiwan".

In a statement on Sunday, the Foreign Ministry said it had lodged a protest with the United States over the Taiwan content of the act and expressed its strong opposition.

Taiwan is Chinese territory and purely an internal matter, the ministry said.

It noted that the part of the defense policy bill referring to Taiwan was not legally binding, but said it was an interference with China's internal affairs that China could not accept.

"We urge the US side to abide by its promises made to China on the Taiwan issue, stop US-Taiwan military contacts and arms sales to Taiwan, to avoid damaging Sino-US ties and peace and stability in the Taiwan Straits."

Obama signed the policy bill into law though he said he was disappointed in many aspects, the White House announced on Friday.

The wide-ranging National Defense Authorization Act (NDAA), which was passed by both the House and the Senate with veto-proof majorities earlier this month, lays restrictions on transferring detainees out of the Guantanamo Bay facility in Cuba, ensuring that Obama will not be able to fulfill his goal of closing it before he leaves office.

It authorizes $618.7 billion in spending, including a troop pay raise of 2.1 percent, though Obama has requested only a 1.6 percent pay raise.

It also calls for $3.2 billion more in base defense funding than Obama had requested, plus an additional $5.8 billion in White House-requested war dollars.

As for the size of the Army and Marine Corps, the new bill authorizes 476,000 active-duty soldiers (16,000 more than requested) and 185,000 Marines (3,000 more than requested).

Obama said despite his disappointments, he signed the bill because it "authorizes fiscal year 2017 appropriations principally for the Department of Defense and for Department of Energy national security programs, provides vital benefits for military personnel and their families, and includes authorities to facilitate ongoing operations around the globe".

However, "Congress again failed to enact meaningful reforms to divest unneeded force structure, reduce wasteful overhead and modernize military healthcare," Obama said.

On the campaign trail, US President-elect Donald Trump promised a massive military buildup, including boosting the Army to 540,000 active-duty soldiers, increasing the Navy to 350 warships and adding 1,200 Air Force fighter jets.