China's Ministry of National Defense on Thursday voiced firm opposition to recent U.S. remarks on Taiwan's so-called ultimate political status, saying separatist activities seeking "Taiwan independence" represent the gravest challenge to the post-war international order.

Zhang Xiaogang, a ministry spokesperson, made the remarks at a press conference in response to a reporter's question regarding comments by the "American Institute in Taiwan." The U.S. organization had claimed that post-war documents such as the Cairo Declaration and the Potsdam Proclamation did not determine Taiwan's ultimate political status.

Zhang emphasized that Taiwan's return to China was an integral part of the outcomes of the victory of World War II and the post-war international order.

He pointed out that both the Cairo Declaration in 1943 and the Potsdam Proclamation in 1945 clearly affirmed that Taiwan was to be returned to China, with Japan's Instrument of Surrender in 1945 reaffirming these provisions. Zhang stressed that these international legal documents confirmed China's sovereignty over Taiwan.

"As a signatory of the Cairo Declaration and the Potsdam Proclamation, the United States is fully aware of the historical and legal fact that Taiwan belongs to China, yet it has brazenly revived the fallacy of so-called 'undetermined status,'" he said.

"Separatist activities seeking 'Taiwan independence' pose the gravest challenge to the post-war international order and the biggest threat to peace and stability across the Taiwan Strait," he said.