Meanwhile, the U.S. Navy said Saturday that an aircraft carrier group led by the USS Theodore Roosevelt had entered the disputed South China Sea to "ensure freedom of the seas".

Lii Wen, the director of the ruling Democratic Progressive Party's chapter on the Matsu islands, said China "is exerting pressure with non-military means and we should cautiously respond through legal institutions and law enforcement".

Taiwan's defence ministry said eight Chinese bomber planes capable of carrying nuclear weapons, four fighter jets and one anti-submarine aircraft entered its south-western air defence identification zone on Saturday.

In the US's first public remarks on Taiwan since Mr Biden came into power, the US State Department reaffirmed its "rock-solid commitment" to helping it defend itself.

The announcement comes just days after Joe Biden was sworn in as U.S. president.

But diplomatic cables declassified last summer show that in July 1982, senior State Department official Lawrence Eagleburger told the American representative in Taipei, James Lilley, that US willingness to reduce arms sales to Taiwan was conditioned on China's commitment to a peaceful resolution of cross-strait differences.

The same day a U.S. aircraft carrier group sailed into the South China Sea on a "freedom of navigation" exercise.

"The United States notes with concern the pattern of ongoing PRC attempts to intimidate its neighbours, including Taiwan", he said in a statement, in reference to the People's Republic of China. It says the U.S. urges China to cease its military, diplomatic, and economic pressure against Taiwan and instead engage in dialogue with Taiwan's democratically elected representatives.

While there's been no word from Beijing yet, the seemingly aggressive move comes at a time when tensions between China and the United States are rising, with Washington's strengthening support for Taiwan playing a significant role.

In another sign of support for Taiwan, the island's de-facto ambassador to Washington, Hsiao Bi-khim, was an invited guest at Biden's inauguration.

China refrained from flying into Taiwan's south-west air defence identification zone for years, even though it had the right to do so - such zones are not recognised in worldwide law.

"This was a message by the Biden administration to make crystal clear to China that it is not compromising on the Taiwan issue", said Yasuhiro Matsuda, professor of global politics at the University of Tokyo.

Although Taiwan is officially recognised by only a handful of nations, its democratically elected government has strong commercial and informal links with many countries.

Some of those targeted had roles in deepening ties with Taiwan, including Alex Azar, the former secretary of health and human services, and former undersecretary of state Keith Krach, who both visited Taiwan previous year; and Kelly Craft, the outgoing ambassador to the United Nations, who held a video call last week with Taiwan's president, Tsai Ing-wen.

In 1982, former President Ronald Reagan also made six security assurances to Taiwan, including that the United States pledges not to set a date for ending arms sales to the island, and that it would neither consult Beijing on any arms sales nor revise the TRA. She also called on the USA government to "prudently and properly handle issues relating to Taiwan".

"And that is a commitment that will absolutely endure in the Biden administration. We will make sure that Taiwan has the ability to do that", Blinken said during the confirmation hearing of the Senate Foreign Relations Committee.