Taiwan President Tsai Ing-wen, in an interview with CNN, confirmed that U.S. troops are on the island to train Taiwanese forces, the U.S. news channel reported Wednesday, triggering a harsh reaction from mainland China.

While avoiding clarifying how many U.S. military personnel are on the self-ruled island, which Beijing regards as a renegade province awaiting reunification by force if necessary, Tsai was quoted as saying the number was "not as many as people thought."

The Wall Street Journal reported early this month that a U.S. special-operations unit and a contingent of Marines have been secretly operating in Taiwan to train military forces there as part of efforts to shore up the island's defenses amid concerns regarding potential Chinese aggression.

Citing U.S. officials, the U.S. newspaper said the U.S. forces have been operating in Taiwan for at least a year.

In the interview with CNN on Tuesday, Tsai said, "We have a wide range of cooperation with the U.S. aiming at increasing our defense capability."

On Thursday, Chinese Foreign Ministry spokesman Wang Wenbin called on Washington not to interfere in the country's "internal affairs," saying, "We resolutely oppose any form of official exchanges and military ties between the United States and Taiwan."

The U.S. military has "provoked and disrupted the situation, sent serious wrong signals to the Taiwan independence forces and threatened peace and stability in the Taiwan Strait," Wang added.

Taiwan and mainland China have been separately governed since they split as a result of a civil war in 1949.

The United States switched its diplomatic recognition from Taiwan to Beijing in 1979. Washington, however, remains committed to unofficial relations with Taipei while continuing to assist the island in maintaining a sufficient self-defense capability.

With China stepping up military and diplomatic pressure on the island, the U.S. administration of President Joe Biden has been urging Beijing to stop its efforts to intimidate Taiwan.

The U.S. military, meanwhile, has been warning of possible Chinese aggression toward Taiwan, with Adm. John Aquilino saying in March before assuming leadership of the U.S. Indo-Pacific Command that the threat is "much closer to us than most think."

Related coverage:

North Korea raps Biden's pledge to defend Taiwan if China attacks

FOCUS: Democracies draw closer to Taiwan as China more belligerent

Taiwan leader pledges defense of island in face of Chinese pressure