The result was announced by the parliamentary speaker after a final vote on the bill, which falls well short of the government's proposed budget of nearly $40 billion.

Taiwanese lawmakers have been 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 seize it forcibly.

The Kuomintang (KMT), which favours closer ties with China, and the Taiwan People's Party (TPP) announced on Friday they would be willing to raise their original spending proposal to a maximum NT$780 billion (nearly $25 billion) for US arms only.

The KMT and the TPP control Taiwan's 113-seat parliament. Only 107 lawmakers were present for the vote, which passed with 59 in favour.

President Lai Ching-te's government, which has vowed to increase overall defence spending to more than three percent of GDP this year, has proposed NT$1.25 trillion for weapons purchases, including US arms as well as Taiwan-made drones and other items.

The special funds would be spread out over eight years and would be in addition to normal defence spending that is included in the government's annual budget.

Lawmaker Chen Kuan-ting, who belongs to Lai's Democratic Progressive Party, accused KMT leaders of "trying to disarm Taiwan" by excluding domestic procurement from the budget.

"If we restrict ourselves only to US arms purchases, then if one day Taiwan is encircled, Taiwan is blockaded, how are we going to maintain our ammunition supply and how are we going to sustain our combat capacity?" Chen said.

KMT lawmaker Hsu Chiao-hsin said the party supported "reasonable defence buildup and arms procurement", but could not "accept lumping together arms sales, commercial purchases, and commissioned production".

Months of infighting have left the KMT divided, with the party's chairperson Cheng Li-wun -- who has drawn criticism from inside and outside the KMT for being too pro-China -- pushing for the allocation of NT$380 billion for US weapons, with the option for more acquisitions.

- Missiles and artillery -

As pressure from the United States -- Taiwan's most important security backer -- mounted, however, senior KMT lawmakers demanded a much higher budget than the one initially proposed by the party.

Taiwan's parliament previously gave the government a green light to sign US agreements for four weapons deals.

The weapons -- M109A7 self-propelled howitzers, Javelin anti-armour 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 KMT was "willing to fully support" a second phase of arms sales worth more than $15 billion that the defence ministry has told lawmakers would include "Patriot missiles, Hellfire (missiles), and related counter-drone defence systems", party caucus leader Fu Kun-chi said before the vote.

The result was a "huge blow to Lai", said Lev Nachman, a political science professor at National Taiwan University.

"This is much less than (his) proposed budget, but it is still greater than zero," he said.

Taiwan analyst Wen-Ti Sung said the KMT had shown just enough commitment to US-Taiwan security cooperation to "silence doubters" of the party, including in Washington, but "not too much to ruffle feathers in Beijing".

It comes days before US President Donald Trump is due to arrive in Beijing for a summit with his Chinese counterpart Xi Jinping, who has warned the United States against sending more weapons to Taiwan.

Cheng recently went to China, where she met with Xi, and she has expressed hopes to travel to the United States in June.