The activist, Li Ming-che, is a community college worker known for supporting human rights.
China said on Friday that a Taiwan rights activist has been arrested on suspicion of subversion and has confessed to harming state security, as Taiwan said the charges were vague and unconvincing.
The case has strained already poor relations between China and Taiwan, which have cooled since Taiwan President Tsai Ing-wen took power last year, because she refuses to concede that the self-ruled island is part of China.
The activist, Li Ming-che, is a community college worker known for supporting human rights. He went missing in China, which views neighbouring Taiwan as a wayward province, on March 19, and China later confirmed his detention.
In a short statement carried by the official Xinhua news agency, China's Taiwan Affairs Office said that Li had been formally arrested by state security authorities in the southern province of Hunan on suspicion of subversion of state power.
State security authorities had ascertained that since 2012, Li had entered China multiple times, the government said.
While in China, he had "colluded with relevant people in the mainland, formulated action programmes, established illegal organisations and plotted and enacted activities to subvert the power of our authorities", it added, without giving details.
"After being interrogated, Li Ming-che confessed to engaging in activities to harm our state security, and the judicial authorities will handle the case in accordance with the law."
It is not clear if Li has been allowed to retain a lawyer. China's Ministry of State Security has no publicly listed contact details or website.
Taiwan's Mainland Affairs Council, which handles relations with China, said in a statement the charges were vague and that China had provided no evidence.
"This cannot convince the people of Taiwan," it said. "We do not agree with any of the alleged charges China has against Li Ming-che."
Taiwan demands that China announces what evidence it has in the case as soon as possible and allow family members to visit, it added.
Li's wife, Li Ching-yu, was looking at the report, family friend Cheng Hsiu-chuan said.
She has said from the beginning that she rejected the allegations made by Chinese authorities, Cheng, head of the community college where Li worked, told Reuters.
Li's family and the Taiwan government have previously expressed frustration at not being told where Li was being held.
Li's wife was barred from travelling to China last month.
China has never renounced the use of force to bring Taiwan under its control, while proudly democratic Taiwan has shown no interest in being run by Communist Party rulers in Beijing.
Defeated Nationalist forces fled to Taiwan in 1949 after losing a civil war with the Communists.
(This article has not been edited by DNA's editorial team and is auto-generated from an agency feed.)
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