Beijing, China - Officials in Beijing have denounced a joint statement made by the US and Japan that opposed China's claims to and militarization of the South China Sea.

China's anger comes days after the US and Japan signed a joined statement in which the Trump administration and the government of Prime Minister Shigeru Ishiba pledged deeper cooperation and directly denounced Beijing.

In the joint statement, both leaders reiterated their opposition to what they called China's "force" and "coercion," as well as "the PRC’s unlawful maritime claims, militarization of reclaimed features, and threatening and provocative activities in the South China Sea."

Trump and Ishiba also put a focus on "the importance of maintaining peace and stability across the Taiwan Strait as an indispensable element of security and prosperity for the international community."

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"They encouraged the peaceful resolution of cross-Strait issues, and opposed any attempts to unilaterally change the status quo by force or coercion. The two leaders also expressed support for Taiwan’s meaningful participation in international organizations."

Beijing hit back against the joint statement during a daily press conference on Monday, condemning what it calls "attacks and smears" against China, and said that it had made "solemn representations" to both countries.

Responding to a query from China's state-owned news agency Global Times, foreign ministry spokesperson Guo Jiakun accused the US and Japan of "scaremongering" and said that China "deplores and firmly opposes" the statement.

Spokesperson Guo specifically took issue with the US and Japan's stance on Taiwan, which he said is an affair "at the core of China's core interests" that should not be interfered with.

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"If relevant countries truly care about peace and stability in the Taiwan Strait, what they should do is to uphold the one-China principle, and unequivocally oppose 'Taiwan independence,'" Guo told reporters.

Beijing has long held that Taiwan is not a sovereign country and should not receive the rights of one, as it is part of China. This has led to countless sanctions against US firms that support and supply the democratically-elected government on the island.

Guo called on the US to respect China's sovereignty, commit to the one-China principle, and stop "interfering" in Beijing's domestic policy.

He also said the US should "respect China's territorial sovereignty and maritime rights and interests, stop manipulating China-related issues, and take concrete actions to play a constructive role for the peace and development in the region."