"The United States opposes unilateral actions by any party that are aimed at altering the status quo, including anything related to force or coercion," State Department spokesman Robert Palladino told reporters.

"Beijing should stop its coercive efforts and resume dialogue with the democratically elected administration" in Taipei, he said.

Beijing -- which considers Taiwan part of its territory awaiting reunification -- has stepped up its jet and warship crossings near the island since the 2016 election of Beijing-skeptic President Tsai Ing-wen.

But going a step further, Taiwan's defense ministry said that two Chinese J-11 fighter jets took the highly unusual step Sunday of crossing the median line in the Taiwan Strait that divides the mainland from the island.

Taiwan scrambled its own aircraft and protested the "intentional, reckless and provocative action."

The United States, like the vast majority of countries, recognizes only Beijing, but it maintains a close relationship with Taiwan.

Under the 1979 Taiwan Relations Act passed by the US Congress, Washington is legally obliged to provide the island with the means to defend itself.

National security advisor John Bolton stressed US commitment for the Taiwan Relations Act in a tweet on Monday amid events to mark the law's 40th anniversary.

"Chinese military provocations won't win any hearts or minds in Taiwan, but they will strengthen the resolve of people everywhere who value democracy. The Taiwan Relations Act and our commitment are clear," he wrote.