US president-elect Donald Trump's choice of James Mattis, a retired general with a reputation as a hard-liner, as secretary of defense might lead to more uncertainty and confrontation in China-US military ties, Chinese experts said.

Trump has officially nominated the former four-star Marine Corps general as head of the Pentagon, making him the first general to run the Pentagon since George Marshall in 1950.

Mattis adds another staunch conservative to Trump's list of Cabinet nominees and high-level advisers, including Jeff Sessions as attorney general, Michael Flynn as national security adviser and Mike Pompeo as CIA director.