Li Ching-yu (C), a wife of Taiwanese human rights activist Li Ming-che, who is detained in China, speaks to media after she was rejected to board a plane to Beijing at Taoyuan International Airport, Taiwan April 10, 2017. REUTERS/Fabian Hamacher

By Damon Lin and Fabian Hamacher

TAOYUAN, Taiwan (Reuters) - The wife of a Taiwan activist accused China of "political conspiracy" on Monday after she was barred from travelling to the mainland to support her husband who has been detained there on suspicion of endangering national security.

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 renegade province, on March 19.

More than a week later, China's Taiwan Affairs Office said Li had been detained on suspicion on endangering national security but gave no information on his whereabouts.

Li's wife, Li Ching-yu, had been scheduled to fly to Beijing but told reporters at Taiwan's international airport her permit to enter the mainland had been cancelled.

"I am a weak woman who wants to visit. Is it really necessary for the Chinese government to use such great force to prevent this?" Li said.

"This action confirms to the outside world that there is political conspiracy behind the Chinese government's arrest of Li Ming-che."

Li's detention has put another strain on ties between Taipei and Beijing, which have cooled since Taiwan President Tsai Ing-wen took power last year because she refuses to concede that the island is part of China.

Tsai also leads the Democratic Progressive Party (DPP), which traditionally advocates independence for Taiwan, a red line for Beijing.

Beijing has never renounced the use of force to bring Taiwan into its fold, while proudly democratic Taiwan has shown no interest in being run by Communist Party rulers in Beijing.

Over the weekend, Chinese state media reported that a letter written by Li Ming-che had been delivered to his family on Friday on humanitarian grounds.

However, according to Li Ching-yu, the letter was a copy that she could not verify was from her husband and was delivered via unofficial channels by an individual who said the people holding her husband should be seen as "kidnappers".

The DPP admonished Beijing, saying that its moves ran counter to the goal of normal exchanges between the two sides.

"Moreover, (China) should not bypass our government units, and allow the case to become more complicated by the use of unauthorized private entities or individuals to inform the family about the disputed case," the DPP said in a statement.

Taiwan activists have linked Li's detention to a new law targeting foreign non-governmental organisations in China, which grants powers to police to question organisation workers, monitor their finances and regulate their work.

Taiwan citizens use a special entry permit issued by China to travel there because China does not recognise Taiwan passports.

(Additional reporting by J.R. Wu in TAIPEI and Christian Shepherd in BEIJING; Editing by Robert Birsel and Nick Macfie)