Beijing said on Thursday that the United States and Japan had "smeared and attacked" China during a Washington summit, where US President Joe Biden and Japanese Prime Minister Fumio Kishida unveiled their countries' biggest upgrade in defence ties.

Biden and Kishida unveiled plans on Wednesday to restructure the US military command in Japan, the biggest such change since the 1960s.

The move is aimed at making US and Japanese forces more nimble in the event of threats, such as a Chinese invasion of Taiwan.

Biden insisted that the military upgrade in China's backyard was "purely defensive" but has made no bones about his desire to create alliances to counter Beijing.

In response to a question on Kishida's visit and the upgrade in ties, foreign ministry spokeswoman Mao Ning said the United States and Japan had "smeared and attacked China on Taiwan and maritime issues, which was grossly interfered in China's internal affairs, and seriously violated the basic norms governing international relations".

Mao said China was strongly dissatisfied with and firmly opposed to this and has lodged solemn representations with relevant parties.