TAIPEI (Reuters) - Taiwan’s ruling party on Wednesday urged citizens to avoid visiting Hong Kong after a person from Taiwan was detained in China on state security charges, as Hong Kong’s protests add to already tense relations between Taiwan and Beijing.

FILE PHOTO - An audience waves Taiwanese flags during the National Day celebrations in Taipei, Taiwan October 10, 2018. REUTERS/Tyrone Siu

China said Lee Meng-chu, an adviser from a small township in Taiwan, who had been missing since Aug. 19 after traveling to the southern Chinese city of Shenzhen, was suspected of “engaging in criminal acts that endanger state security”.

Lee had distributed photographs of Hong Kong’s protests and Chinese troops gathering on China’s border with the city before his disappearance, Taiwan’s official Central News Agency has reported.

“The Democratic Progressive Party urges citizens to avoid visiting Hong Kong and China due to tough internal situations,” Taiwan’s ruling party said in a statement.

It expressed “strong condemnation” of Lee’s detention.

“If you have to visit these areas, you must pay serious attention to safety and report whereabouts to your families and friends at all times,” the party said.

The detention comes amid a delicate time for cross-strait relation with the protests in Chinese-ruled Hong Kong posing the biggest challenge for Communist Party rulers in Beijing since President Xi Jinping took power in 2012.

China claims self-ruled Taiwan as its own and has vowed to bring the island under its control, by force if necessary.

China has suggested the island could be ruled under a formula similar to Hong Kong’s “one country, two systems” arrangement, which guarantees certain freedoms, but Hong Kong’s protests have raised questions about the formula.

Beijing has accused Taipei of supporting the Hong Kong protests. Taiwan denies that.

In Beijing, Ma Xiaoguang, spokesman for China’s Taiwan Affairs Office, said Lee was being investigated “in accordance with the law”. He gave no other details.

Taiwan’s Mainland Affairs Council demanded Beijing give a “full explanation”, including information on Lee’s whereabouts and the charge he faces.

“The mainland authority has not informed us or his family, nor given explanation,” the council said.

Despite the tension between Taiwan and Beijing, many Taiwan people visit and do business in China, one of the island’s main trading partners.

Li Ming-che, a community college lecturer and an activist at a human rights organisation in Taiwan, was found guilty of subversion after visiting China in 2017.