Beijing on Thursday said 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-ever upgrade in defence ties.

"Ignoring China's grave concerns, the US and Japan have smeared and attacked China on Taiwan and maritime issues, grossly interfered in China's internal affairs, and seriously violated the basic norms governing international relations," foreign ministry spokeswoman Mao Ning told a regular press conference.

Biden and Kishida unveiled plans 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.

The US president 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, Mao said China was "strongly dissatisfied with and firmly opposed to this and has lodged solemn representations with relevant parties".

"The US-Japan relationship should not target or harm other countries' interests, and should not undermine regional peace and stability," she said.

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