TAIPEI (Reuters) - Taiwan President Tsai Ing-wen vowed on Wednesday to boost national security, saying her government would not submit to Chinese suppression as Beijing ramps up pressure to assert its sovereignty over the self-ruled island.

Slideshow ( 4 images )

Tsai’s remarks came ahead of island-wide local elections in late November that are seen as a bellwether for her ruling party’s performance in presidential elections due in 2020.

“At this time, China’s intimidation and diplomatic pressure not only hurts relations between both sides, but seriously challenges the peaceful stability in the Taiwan Strait,” she said in a National Day speech in Taipei.

Taiwan will increase its defense budget every year to ensure it can defend its sovereignty, Tsai said, by upgrading military capabilities and self-sufficiency, including resuming domestic development of advanced training aircraft and submarines.

China, which views Taiwan as a wayward province, has increased military and diplomatic pressure on Taipei, leading to a difficult period for the president and her independence-leaning Democratic Progressive Party.

Three former allies - El Salvador, Burkina Faso and Dominican Republic - switched their allegiances to Beijing this year, and the Chinese military has stepped up encirclement drills around Taiwan, which Taipei has denounced as intimidation.

Taiwan must work with other countries to build a coalition to defend democracy, Tsai said, thanking the European Parliament and the United States for their support.

The U.S. State Department approved the sale to Taiwan of spare parts for F-16 fighter planes and other military aircraft worth up to $330 million last month, a move China said jeopardizes Sino-U.S. cooperation.

China has never renounced the use of force to bring Taiwan under its control and regularly calls the island its most sensitive issue in its ties with the United States.

Relations with Beijing have nosedived since Tsai came into office in 2016, with China suspecting that she wants to push for formal independence, a red line for Beijing.

Ma Xiaoguang, a spokesman for China’s Taiwan Affairs Office, said Taiwan independence was “doomed to fail”.

“Fraught with the ‘two Chinas’ separatist fallacy and confrontational thinking, the speech exposed the evil intentions to contain the mainland with the help of anti-China forces in the West,” Ma said in a statement late on Wednesday.

For her part, Tsai has repeatedly emphasized maintaining the status quo since coming to power.

On Wednesday, she called for a multinational effort to fight some types of infiltration, such as the circulation of fake news by certain countries that she did not name.

“I would like to pledge to everyone that we will not rashly increase antagonism, but we won’t submit or yield,” she said.