Donald Trump's administration has approved $1.3 billion worth of arms sales to Taiwan, a US government official said Thursday, in a move likely to provoke the ire of Beijing which considers the island a rebel province.

The US official emphasised that there is “no change to our longstanding 'One China' policy” — stating that there is only one China and that Taiwan is part of it -- which Beijing says is a prerequisite for maintaining relations.

Announcement of the sale comes at a sensitive moment for the US and China, as President Trump is working to establish a partnership over trade differences and efforts to curb North Korea's nuclear weapons program.

Taiwan is a self-ruling democracy but China sees it as part of its territory to be reunified, by force if necessary.

The US is the island's most powerful ally and arms supplier despite having no official relations with Taipei after switching recognition to Beijing in 1979.

The latest plans are consistent with terms of the 1979 Taiwan Relations Act, the US official said, under which Washington keeps trade ties and sells Taipei weapons to “maintain a sufficient self-defence capability”.

Taiwan thanked the US for its continued commitment under the legislation and said the deal “increases Taiwan's confidence and ability to maintain the status quo of peace and stability across the Taiwan Strait”.

“We will continue to seek constructive dialogue with Beijing, and promote positive developments in cross-strait relations,” said a statement from Taiwan's Presidential Office.

“At the same time, we will continue to increase our defence investments, including in indigenous defence industries and defence-related research, in order to demonstrate our commitment to Taiwan's self-defence,” it added.

The defence ministry said the sales will boost the island's air and sea combat capabilities.

The Trump administration has formally notified Congress of the defence sales comprised of seven parts, the US official said, which are “based on an assessment of Taiwan's defence needs” and include upgrading defence systems from analog to digital.

The last US arms sale to Taiwan was in December 2015.

Concerns that Taiwan would become a bargaining chip were raised soon after Trump's election, when he suggested he may abandon the “One China” policy that underpins US-China relations, unless he could strike better deals with Beijing.

Just after winning election, Trump infuriated China by accepting a congratulatory call from Taiwan's Beijing-sceptic president Tsai Ing-wen, smashing decades of diplomatic precedent.

But once in office the president unequivocally endorsed the “One China” policy during a visit by Chinese leader Xi Jinping.

China "outraged" by $1.42 bln planned US arms sales to Taiwan

Relations between Taipei and Beijing have rapidly deteriorated since Tsai took the reins, ending an eight-year cross-strait rapprochement.

China's embassy to the United States has urged Washington to revoke its “wrong decision” immediately and halt $1.42 billion worth of planned arms sales to Taiwan.

“The Chinese government and Chinese people have every right to be outraged,” the embassy said in a statement released late on Thursday. The sale sends a very wrong message to “Taiwan independence” forces, it said.

China's anger over Washington's decision risks damaging US President Donald Trump's attempts to seek additional help from China to rein in North Korea's nuclear and missiles programmes.

“The wrong move of the US side runs counter to the consensus reached by the two presidents in Mar-a-Lago and the positive development momentum of the China-US relationship,” China's embassy said, referring to Trump's Florida resort where the US leader met Chinese President Xi Jinping in April.

Trump had previously played up his personal relationship with Xi after that meeting, calling him a “good man.”

The United States is the sole arms supplier to Taiwan, which China deems its own. It has never renounced the use of force to bring the self-ruled island under its control.

US State Department spokeswoman Heather Nauert told reporters on Thursday the administration had told Congress of seven proposed sales to Taiwan, the first such sales under the Trump administration.

The package includes technical support for early warning radar, high speed anti-radiation missiles, torpedoes and missile components.

Beijing's relationship with Taiwan has been frosty since president Tsai Ing-wen took power in Taipei last year. Tsai leads an independence-leaning party that refuses to recognise the “one China” policy.

Tsai's office said on Friday the sale increased Taiwan's confidence and ability to maintain peace and stability across the Taiwan Strait.