In an unusually strong and direct message a senior Taiwanese security official has said a Chinese blockade of Taiwan or the seizure of an offshore island would be considered an act of war and that it would not surrender.

While Taiwan President Tsai Ing-wen and others in her administration have repeatedly said that while they want peace they would defend themselves if attacked, the details of what Taiwan would consider an attack warranting a response have generally been left unsaid, given the many scenarios.

Chinese military action might not be as straightforward as a full frontal assault on Taiwan: it could include actions like a blockade to try to force Taiwan to accept China's rule, strategists say.

The tension between Beijing, which views Taiwan as its own territory, and Taipei has spiked since U.S. House Speaker Nancy Pelosi visited the island in early August.

To show its anger, China mounted military exercises around Taiwan that included firing missiles and steps to mount a blockade. China has since then continued its military activities, though on a smaller scale.

That has focused attention on Taiwan and the capitals of friendly countries, like the United States and Japan, on how any conflict with China could play out, and how Taiwan and its allies might respond.

The senior Taiwanese security official, speaking on condition of anonymity, said China's drills after the Pelosi visit had shown what might happen in case the worst came to the worst and focused thought on how Taiwan would react.

"A blockade is an act of war; seizing an offshore island is an act of war," the official said, adding Taipei believed Beijing was unlikely to take either of those actions at the moment.

"Their only purpose to seize (offshore islands) is to force us to negotiate or surrender. But we will not surrender or negotiate."

Short of an outright invasion, many military strategists, and even Taiwan's defense ministry, have said China could try and seize one of Taiwan's offshore islands, like the Kinmen and Matsu archipelagos, just off China's coast.

"Those are military actions. There is no room for ambiguity," the official said.

China's Taiwan Affairs Office did not immediately respond to a request for comment.

'Building deterrence'

The official said Taipei did not rule out the possibility of Beijing launching large-scale military exercises near Taiwan next year when the island gears up for a presidential election in early 2024.

"This is what we are worried about at the moment," the official said, adding other possible Chinese actions could include stepping up its "grey-zone" tactics near Taiwan including incursions with militia boats or cyberattacks.

The official said countries other than the United States, which sails warships through the Taiwan Strait about once a month, should show Beijing that an attack on Taiwan would not go unanswered.

"Building up deterrence is very important. Not just America, European countries and Japan should join the force of deterrence."

U.S. President Joe Biden said in comments broadcast on Sunday that U.S. forces would defend Taiwan in the event of a Chinese invasion, his most explicit statement on the issue.

With the world's most advanced semiconductors produced in Taiwan, it is in the world's interest to ensure stability, the official said.

"Pressure in the Taiwan Strait is pressuring chip supplies."

Tsai, who has said Taiwan would not provoke China or "rashly advance," has made bolstering defense a priority, including a double-digit increase in defense spending next year.

While China has said it prefers peaceful "reunification" and has offered Taiwan a Hong Kong-style autonomy deal, it has never renounced the use of force to bring the island under its control.

Taiwan's democratically elected government says only Taiwan's people can decide their future.