Any unprovoked attack on Taiwan will result in a "resolute reaction" from Washington, US Congressman Rob Wittman said Friday during a visit to Taipei.

China claims self-ruled Taiwan as its territory to be taken one day, by force if necessary, and it has ramped up pressure in recent years with near-daily air incursions and frequent military drills around the island.

Wittman, a Republican, is vice chair of the House Armed Services Committee, which oversees funding for the US military, and is leading a delegation on a three-day visit to Taiwan.

"President Tsai (Ing-wen), know that any, any hostile, unprovoked attack on Taiwan will result in a resolute reaction from the United States," he said during a speech Friday.

Wittman said peace and stability in the Indo-Pacific region is built on "a foundation of strength".

"We know strength is the best deterrence to anyone that may think there is an opportunity to act badly in this region."

While the United States officially recognizes Beijing over Taipei, it is Taiwan's key ally, providing weapons and aid to boost its defenses against an increasingly aggressive China.

Wittman also promised Friday to help resolve the delivery backlog of weapons purchased by Taiwan.

This week, US President Joe Biden's administration approved direct military aid to Taiwan for the first time under a financing program for foreign governments.

But the State Department insisted this move did not imply any recognition of Taiwanese sovereignty — a red line for Beijing.

This followed the approval in July of $345 million in military aid to Taiwan from leftover US stockpiles.