Washington DC - A US senator said Monday it is "very important" for Taiwan to approve a special defense spending bill, as Washington dials up pressure on the island to invest more in its own military capabilities.

"Passing of the special defense 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 Taiwanese President Lai Ching-te.

Taiwan's parliament is debating proposals for special defense spending aimed at boosting the island's ability to defend itself against a potential Chinese attack.

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

As US pressure grows, some KMT lawmakers are pushing for a much higher budget than the one proposed by the party, signaling an internal split over defense.