China insisted Wednesday that Taiwan had no right to join the United Nations, after the United States ratcheted up tensions with a call for the democratic island to have greater involvement in the world body.

In a statement marking 50 years since the UN General Assembly voted to seat Beijing and boot out Taipei, US Secretary of State Antony Blinken said Tuesday he regretted that Taiwan had been increasingly excluded on the world stage.

"As the international community faces an unprecedented number of complex and global issues, it is critical for all stakeholders to help address these problems. This includes the 24 million people who live in Taiwan," Blinken said.

"Taiwan's meaningful participation in the UN system is not a political issue, but a pragmatic one," he said.

"That is why we encourage all UN member states to join us in supporting Taiwan's robust, meaningful participation throughout the UN system and in the international community."

China considers Taiwan -- where nationalist forces fled in 1949 after losing a civil war to the communists -- to be a province awaiting reunification, by force if necessary.

It responded to Blinken's statement with strident, albeit familiar, statements emphasizing its position that Taiwan's government had no place on the global diplomatic stage.

"Taiwan has no right to join the United Nations," Ma Xiaoguang, spokesman for the Taiwan Affairs Office in Beijing, told reporters.

"The United Nations is an international governmental organization composed of sovereign states... Taiwan is a part of China."

The United States has long called for Taiwan's inclusion in UN activities.

Defense of Taiwan

But the latest statement adds to an escalation of diplomatic rhetoric and military posturing over Taiwan.

China is regularly setting records for its number of warplane flights near the island.

US President Joe Biden last week told a televised forum that the United States was ready to defend Taiwan from any Chinese invasion.

Those comments were quickly walked back by the White House amid warnings from China, continuing a strategy of ambiguity on whether it would intervene militarily if China attacked.

The United States switched recognition in 1979 to Beijing.

But Congress at the same time approved the Taiwan Relations Act that obligated the supply of weapons to the island for its self-defense.

Blinken on Tuesday reiterated that the United States still recognized only Beijing.

But he emphasied the democratic credentials of the island of 23 million people.

"Taiwan has become a democratic success story," Blinken said. "We are among the many UN member states who view Taiwan as a valued partner and trusted friend."

Blinken pointed to Taiwan's exclusion from meetings associated with the International Civil Aviation Organization and the World Health Organization.

He noted that Taiwan was hailed for its "world-class" response to Covid-19 -- which largely spared the island after early intervention -- and that tens of millions of passengers go through Taiwanese airports each year.

Taiwan President Tsai Ing-wen welcomed Blinken's remarks.

"Grateful for #US support for expanding #Taiwan's international participation," she said on Twitter.

"We stand ready to work with all like-minded partners to contribute our expertise in international organizations, mechanisms & events."