Taiwanese lawmakers are at loggerheads over how much to spend on improving defence capabilities against a potential attack by China, which claims the island is part of its territory and has threatened to forcibly seize it.

Taiwanese President Lai Ching-te's Democratic Progressive Party and the two opposition parties, which control parliament, are locked in negotiations after reviewing rival budget proposals last week and failing to reach a consensus.

"Passing of the special defence budget is very important to me and my colleagues back in Washington DC," Republican Senator John Curtis told reporters in Taipei, during a visit by a bipartisan Senate delegation.

"We want to make sure that as we invest in this part of the world, that you are also investing and that we're in this together," he said, after the senators met with Lai.

Lai's government has proposed NT$1.25 trillion ($39 billion) in spending on critical defence purchases, including US arms, while the opposition Kuomintang party (KMT) wants to allocate NT$380 billion for US weapons with the option for more acquisitions.

As pressure from the United States -- Taiwan's most important security backer -- grows, some KMT lawmakers are pushing for a much higher budget than the one proposed by the party, signalling an internal split over defence.

Democratic Senator Jeanne Shaheen, who is part of the delegation, said US support for Taiwan "remains strong and enduring".

Shaheen expressed concern at "the increased pressure from Beijing, including military activity around Taiwan that raises the risk of miscalculation".

As part of the two-day visit, the delegation stopped by Taiwan's National Chung-Shan Institute of Science and Technology to look at military drones and equipment in development.

Taiwan has spent billions upgrading its defences. The island maintains its own defence industry but it would be massively outgunned in a conflict with China, and remains heavily reliant on US arms sales.

Earlier this month, Taiwan's parliament gave the government a green light to sign US agreements for four weapons deals, even though funding for these and other arms has not yet been approved.

The weapons -- M109A7 self-propelled howitzers, Javelin anti-armor missiles, TOW 2B missiles and High Mobility Artillery Rocket Systems (HIMARS) -- account for nearly $9 billion of the $11.1 billion arms package announced by Washington in December.

The US Congress, under the Taiwan Relations Act, requires the supply of weapons to the self-governing democracy for its defence.

While the government's NT$1.25 trillion in spending was "essential" for Taiwan's defence, senior DPP lawmaker Wang Ting-yu told AFP on Friday the party could potentially work with NT$900 billion -- if the opposition did not restrict the budget to US arms.