TAIPEI/BEIJING (Reuters) - China must specify the charges against a detained Taiwan human rights activist or release him, his wife, ruling party lawmakers and rights groups in Taiwan said on Wednesday, the latest dispute between China and an island it considers its own.

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China confirmed that Li Ming-che, previously identified by the family name of “Lee”, was in custody and being investigated on suspicion of harming national security, its first response since Li disappeared in China on March 19.

Activists in Taiwan linked Li’s detention to a new law targeting foreign non-governmental organizations in China, which grants broad powers to police to question NGO workers, monitor their finances and regulate their work.

China’s behavior was “completely detrimental to the future of exchanges between the two sides”, said Chiu E-ling, an official with the Taiwan Association for Human Rights, adding that the detention would have a “chilling effect” on ties.

China must disclose Li’s whereabouts, release him if it cannot explain the charges, allow his family and lawyer to visit and ensure he is not abused, she said during a joint news briefing with Li’s wife, Li Ching-yu, other rights watchdogs and lawmakers from the ruling, independence-leaning Democratic Progressive Party (DPP).

The case further strains ties between Taipei and Beijing, which have cooled since President Tsai Ing-wen took power in Taiwan last year because she refuses to concede that the self-ruled island is part of China.

Beijing has never renounced the use of force to take what it regards as a breakaway province, while proudly democratic Taiwan has shown no interest in being run by Communist Party rulers in Beijing.

The DPP at the weekend slammed Beijing for causing “anxiety and panic” for the family by withholding information about Li.

Ma Xiaoguang, spokesman for China’s Taiwan Affairs Office, told reporters Li’s case was being handling in accordance with the law.

“According to what is understood, Taiwan resident Li Ming-che is suspected of engaging in activities endangering national security and is being investigated by the relevant authority,” Ma said. “At present his health is good.”

Ma said Taiwanese people coming to China for “normal” activities did not have anything to worry about and their rights would be protected.

Li, a community college worker known for supporting human rights in China, disappeared after entering China’s Zhuhai city via the Chinese territory of Macau.

Li traveled to China about once a year to see friends and regularly discussed Taiwan’s democratic process, Li Ching-yu said, adding that her husband regularly mailed books to China.

But in August last year, one package was confiscated and his chat account in China was shut down, she said.

“This (Li’s) kind of behavior - based on standards of civilized countries - is innocent,” Li Ching-yu said.