Chinese writer and rights activist Xie Qiang, who signed a 2008 charter calling for sweeping political reform, is incommunicado, believed detained, after receiving an unexpected phone call from police, his friends said.
Xie, who is better known by his pen-name Ma Xiao, sent out a social media message on April 26 that read: "They haven't contacted me in 10 years, and suddenly I get a phone call today. What's going on?"
Since then, Xie, who hails from the central province Hunan but who is resident in Beijing's Songzhuang Artists' Village, hasn't been in contact with friends or family.
"His friends called the Songzhuang police station, but they said there was nobody by that name there," housing rights activist Ni Yulan told RFA on Monday. "That made them even more worried."
"Maybe he wrote something that they thought he shouldn't have written, and now he has been summoned to 'drink tea' or 'disappeared'," she said. "It has been 10 days now, and nobody has told his family anything, so everyone is pretty worried right now."
Ni said Xie is also a veteran rights activist who has paid close attention to the treatment of China's political prisoners over the years.
"He wrote a number of features in recent years about political prisoners," Ni said. "He wanted to improve conditions for them, so he wrote about unfair treatment they received in jail and posted the articles to the relevant websites."
"I was one of them," she said.
Called to 'drink tea'
Sources told RFA that Xie's disappearance came after he was called in to "drink tea" with the state security police, and never reappeared.
Beijing artist Wang Peng is a close friend of Xie's.
"We were still messaging a couple of weeks ago," Wang told RFA. "He was asking me to find him a job, because he wasn't making any income out of the articles he was writing."
"Ma Xiao was always pretty low profile ... he had set up a few websites, and often referred to issues with the ruling Chinese Communist Party," Wang said. "He is kind of a scholarly character."
Wang said Xie had previously been targeted by the government's "stability maintenance" machine, which aims to silence and restrict critics of the ruling party, and that his disappearance could be linked to the forthcoming 30th anniversary of the Tiananmen massacre next month.
"It's 30 years since the June 4, 1989 [massacre] this year, so it's pretty likely that they'll be detaining people like him," Wang said.
Repeated calls to the Songzhuang police station in Beijing's Tongzhou district rang unanswered on Sunday.
Repeated attempts to contact Jia Lijun, head of the state security police for Tongzhou district, were also unsuccessful.
Called for reform
Xie was repeatedly detained and interrogated after signing Charter 08, a 2008 document co-authored by late political prisoner Liu Xiaobo, which called for constitutional government in China.
The questioning focused on his involvement with the overseas-based Chinese Human Rights Defenders (CHRD) network, which translates and compiles human-rights reports from groups and individuals in China.
Xie had attended a human rights training workshop in Thailand in January 2010, and this was also the focus of what he described at the time as "oppressive" interrogation.
Xie, a former civil servant from Hunan's Loudi city, has studied law, and has been an advocate of human rights and democratic reform for many years, according to background information on CHRD's website.
He has written for websites including Minzhu Zhongguo and Boxun, and was active in drafting and circulating public letters and petitions on behalf of Liu Xiaobo and other Charter 08 supporters.
He is the author of two reports on human rights abuses in China, and has organized support for human rights defenders persecuted by the government, CHRD said.
The student-led protests in the spring and early summer of 1989 brought central Beijing to a standstill, with hundreds of thousands of people taking to the streets to call for greater democracy and an end to official corruption.
Public memorials and events marking the anniversary of the bloodshed are forbidden in mainland China, although Hong Kong still holds an annual vigil attended by thousands of people.
Rights activists and dissidents are often held under house arrest, taken on enforced "vacations," or placed under surveillance by state security police ahead of the anniversary on June 4.
Reported by Gao Feng for RFA's Mandarin Service, and by Wong Siu-san and Wen Yuqing for the Cantonese Service. Translated and edited by Luisetta Mudie.