Taiwan has spent billions upgrading its defences as China increases military pressure on the island, which Beijing claims is part of its territory and has threatened to seize by force.

Under US pressure to spend more, Taiwanese President Lai Ching-te's government has proposed $40 billion in funding for critical defence purchases, including US arms, over eight years.

But the Kuomintang (KMT) and the Taiwan People's Party (TPP), which together control parliament, have stalled Lai's proposal and instead drawn up their own stripped-down versions of the spending bill.

The KMT said it proposed allocating more than $11 billion to cover the cost of US arms sales announced in December and pledged to review further weapons purchases once they were approved by US Congress.

The KMT initially announced "NT$350 billion + n" in proposed spending, but hours later increased that to "NT$380 billion + n" without offering a clear explanation for the change.

- 'Contradictions' -

The TPP previously proposed $12.6 billion for military purchases. The three spending bills will be sent to a parliamentary committee for review on Friday.

"We hope to advance arms procurement through a phased, concrete, and clearly defined approach, rather than granting a one-off authorisation, a blank cheque with no spending cap and no detailed content," KMT caucus secretary-general Jonathan Lin told reporters.

"Such an arrangement ensures efficiency while upholding procedural justice, enabling the public to clearly understand the necessity and rationality of each additional expenditure."

Lai's Democratic Progressive Party (DPP) said the KMT's bill contained "contradictions", and could impact the processs for purchasing US weapons.

"In arms procurement, the process usually begins with an intention to purchase, followed by the allocation of a budget," DPP caucus chief executive Chuang Jui-hsiung said.

"Breaking up the NT$1.25 trillion plan for eight years into fragmented pieces could affect the overall timeline for Taiwan's defence procurement."

The United States is Taiwan's most important security backer, and it has been applying pressure to the KMT and TPP to get behind the government's spending bill.

But opposition lawmakers have demanded greater transparency and oversight of the government's planned military purchases.

The KMT said commercial and domestic procurement required "strict scrutiny" and should not be combined with US weapons purchases.

"The KMT has always supported US government-to-government arms sales," the KMT said in a statement on Thursday.

"However, commercial procurement is where corruption and controversy most often occur. These two categories must never be bundled together to pressure the public and the legislature into approving them as a single package."

US President Donald Trump said last month he would decide soon on whether to send more weapons to Taiwan, after Chinese President Xi Jinping warned him not to do so.

Trump is scheduled to travel to Beijing at the end of March to meet Xi.