By Ben Blanchard and Yew Lun Tian

TAIPEI/BEIJING (Reuters) – U.S. President Donald Trump has signed into law an act that requires increased U.S. support for Taiwan internationally, prompting a denunciation by China, which said it would strike back if the law was implemented.

China claims democratic and separately ruled Taiwan as its own territory, and regularly describes Taiwan as the most sensitive issue in its ties with the United States.

While the United States, like most countries, has no official relations with Taiwan, the Trump administration has ramped up backing for the island, with arms sales and laws to help Taiwan deal with pressure from China.

The Taiwan Allies International Protection and Enhancement Initiative (TAIPEI) Act, signed by Trump into law on Thursday with strong bipartisan support, requires the U.S. State Department to report to Congress on steps taken to strengthen Taiwan’s diplomatic relations.

It also requires the United States to “alter” engagement with nations that undermine Taiwan’s security or prosperity.

Taiwan complains that China is poaching the dwindling number of countries that maintain formal ties with Taipei and has prevented it from participating in bodies like the World Health Organization.

China says Taiwan is merely one of its provinces, with no right to the trappings of a state.

Taiwan President Tsai Ing-wen posted a picture on her Twitter page of Taiwan’s flag fluttering next to the U.S. one under the words “Friends in freedom, partners in prosperity”, to welcome Trump’s signing of the law.

It was “a testament to Taiwan-U.S. friendship & mutual support as we work together to address global threats to human health & our shared democratic values”, she wrote in English.

‘RESOLUTE STRIKE’

China has stepped up its military drills around Taiwan in recent weeks despite the outbreak of the coronavirus, which emerged in a central Chinese province late last year and spread rapidly in China and beyond.

Taiwan says China should focus more on fighting the disease than menacing it.

China is already angry about U.S. accusations it poorly handled the coronavirus outbreak, and the new law adds to Sino-U.S. tension.

Chinese foreign ministry spokesman Geng Shuang said the U.S. act contravened international law, was a “crude” interference in China’s internal affairs and obstructed other sovereign states from developing normal relations with China.

“We urge the United States to correct its mistakes, not implement the law, or obstruct the development of relations between other countries and China, otherwise it will inevitably encounter a resolute strike back by China,” Geng said, without giving details.

One of the authors of the act, Senator Cory Gardner, said it was needed to respond to Chinese pressure on, and bullying of, Taiwan.

“This bipartisan legislation demands a whole-of-government approach to ramp up our support for Taiwan, and will send a strong message to nations that there will be consequences for supporting Chinese actions that undermine Taiwan,” he said in a statement.

The United States has been particularly concerned about China hiving off Taiwan’s allies in the Pacific and Latin America, areas of the world Washington traditionally considers its zone of influence.

Taiwan now only has diplomatic relations with 15 countries, almost all small and developing nations like Nauru, Belize and Honduras.

(Reporting by Ben Blanchard; Editing by Robert Birsel)