China on Saturday expressed firm opposition to a joint statement made by the U.S. and Japan on issues relating to China's internal affairs and reaffirmed the country's determination to defend its sovereignty, security and development interests.

U.S. President Joe Biden and Japanese Prime Minister Yoshihide Suga issued the joint statement on Friday, following their meeting at the White House in Washington, D.C. It noted their plan for the "Indo-Pacific" and their exchange of views on the impact of China's actions in the region. They also expressed concerns over issues relating to the East China Sea, the South China Sea and China's Taiwan, Hong Kong and Xinjiang. 

In response, Chinese Foreign Ministry urged the U.S. and Japan to take China's concern seriously, abide by the one-China principle, and immediately stop meddling in China's domestic affairs and harming China's interests.

A ministry spokesperson said in a statement on Saturday that Taiwan and the Diaoyu Islands are part of the Chinese territory, adding that issues relating to Hong Kong and Xinjiang are purely China's internal affairs, and China has indisputable sovereignty over islands in the South China Sea and waters around them.

The spokesperson stressed that the U.S.-Japan joint leaders' statement has grossly interfered in China's domestic affairs and severely violated basic norms governing international relations. 

"China deplores and rejects it. We have stated our solemn position to the U.S. and Japan through the diplomatic channel," said the spokesperson.

The U.S. and Japan are actually ganging up to form cliques and fanning bloc confrontation while talking about "free and open," the spokesperson said. "This anachronistic move runs counter to the aspiration for peace, development and cooperation shared by the overwhelming majority of countries in the region and beyond." 

It will only enable the world to see with increasing clarity the detrimental nature of the U.S.-Japan alliance, which attempts to undermine regional peace and stability, the spokesperson said. 

The Chinese Embassy in the United States issued a statement that said the comments by the U.S. and Japan were beyond the range of bilateral relations.

It harms a third-party's interests, regional countries' mutual understanding and trust, as well as the peace and stability in the Asia Pacific, the embassy stated, adding that the U.S.-Japan statement was in nature an endorsement for separatist activities.

The embassy rebuked the attempt as against the trend of the times and said it would only harm the two countries' own national interests.

Taiwan, Hong Kong and Xinjiang-related issues are purely China's internal affairs, while East China Sea and South China Sea issues concern China's sovereignty and maritime interests, the statement said. It reiterated that these matters are China's fundamental interests that allow no interference.

The Chinese Embassy in Japan on Saturday also expressed strong dissatisfaction and resolute opposition to the U.S.-Japan statement.

The embassy's spokesperson refuted unwarranted accusations against China by the U.S. and Japan, and accused the two countries of violently interfering in China's internal affairs and infringing on China's territorial sovereignty.

Calling the joint statement's so-called claim that "Chinese activities are inconsistent with the international rules-based order" groundless, the spokesperson emphasized that the international system with the United Nations (UN) at its core is the only system in the world, and that the only set of rules in the world is the basic norms governing international relations, based on the purposes of the UN Charter.

The spokesperson noted China's position and claims on East China Sea and South China Sea issues have sufficient historical and legal basis.

"We will continue to firmly safeguard territorial sovereignty and maritime rights and interests, while committing to resolving relevant differences through dialogue and consultation and safeguarding peace and stability in relevant waters."

The spokesperson reiterated that the Diaoyu Islands and its affiliated islands are China's inherent territory. "No matter what Japan and the U.S. say or do, they cannot change the objective fact that the Diaoyu Islands belong to China. 

"The United States and Japan are sticking to the Cold War mentality, deliberately engaging in group confrontation and stirring up political confrontation."

"It is completely going against the trend of the times," the spokesperson said, pointing out that the move by the two countries is against the common expectations of the vast majority of countries, both in the region and globally, for peace, development and cooperation.

The recent negative moves made by the Japanese side on China-related issues have seriously damaged the political mutual trust between the two sides and the efforts to develop bilateral relations, the spokesperson added.

The spokesperson urged the Japanese side to abide by the principles and spirit established in the four political documents between China and Japan, ensure that bilateral relations do not flip-flop, stagnate or backpedal, and not to get involved in the so-called confrontation between major countries.