TAIPEI, Taiwan — Lee Ming-cheh, a human rights advocate from Taiwan who was detained in China in March, has been formally arrested on a charge of “subverting state power,” the Chinese government has announced, amid a continuing crackdown on civil society organizations.

His arrest, announced on Friday, marks the first time the Chinese authorities have charged someone from Taiwan with subversion. Many people in Taiwan fear it will not be the last, and it has added a new strain to the tensions between Beijing and Taipei.

China’s ruling Communist Party has never administered Taiwan but claims it as Chinese territory, to be annexed by force if necessary. The Nationalists who once dominated China fled to the island after losing to the Communists in a civil war in 1949. Today more residents of Taiwan identify themselves as Taiwanese than Chinese, and few support unification with China.

The rift between the two sides has widened since last year, when Tsai Ing-wen was elected president of Taiwan. The Democratic Progressive Party, led by Ms. Tsai, has historically favored formal independence from China.