Chinese authorities were keeping a close watch on artists, college students and other activists ahead of Wednesday's 25th anniversary of the military crackdown on the 1989 pro-democracy movement at Tiananmen Square, activists said.
On the eve of the anniversary, United Nations human rights chief Navi Pillay asked Beijing to reveal the truth about the army's violent suppression of Tiananmen protests and to release dozens of people held in the run-up to the June 4 event.
"It is in the interests of everyone to finally establish the facts surrounding the Tiananmen incidents," Pillay said, noting that Chinese authorities had clamped down on social media, traditional media and Internet users to block discussions on the tragedy.
More than 10 members of Beijing's iconic Songzhuang contemporary arts community have been placed under surveillance by state security police after creating works to commemorate the crackdown by the People's Liberation Army (PLA), residents said on Tuesday.
"They have been very nervous about the art world, and more than 10 households have been put under house arrest or surveillance," Songzhuang artist Zhui Hun told RFA.
"Artists like us with a certain viewpoint or cultural attitude will turn our attention to historical problems," said Zhui.
"Anyone who does something for justice, or with a social conscience, has to pay the price here," he said, adding that controls were much stricter this year than in previous years around the sensitive anniversary.
"Last year they put only me under house arrest, but this year the number has risen to more than 10 households," Zhui said.
Meanwhile, Hong Kong-based poet Meng Lang said a number of his friends across the internal border in mainland China were being targeted by the authorities.
"A lot of friends in mainland China have been targeted by the authorities in this crackdown this year, and some have even been detained, just because they commemorated June 4," Meng said.
"I think such high-pressure tactics are insulting," said Meng, who recently published a book of poems to mark the anniversary in Hong Kong and Taiwan.
Meng, whose poem "Death is Under Way" speaks of guns targeting "glorious faces" with the purpose of exterminating them, said he wanted to mark the anniversary as an act of public memorial.
"I chose 25 poems as a memorial, because it's the 25th anniversary," he said.
Meng's collection comes just days after a group of 23 Chinese artists put out a book of prints of artistic works to mark the crackdown in Hong Kong, which has traditionally been a focus for Tiananmen-related memorial events.
Beijing-based artist Huang Rui, whose work is based on the 64th hexagram of the ancient Chinese "Book of Changes" divination system, said he felt compelled to revisit the scene of the crackdown in his imagination.
"June 4 has become a taboo subject in China, and so this hexagram of the I Ching is also taboo," Huang said. "It is aimed at this historical event, as well as being aimed at a tragic reality suffered by the human race."
Sheng Qi, a second contributor to the book, titled "Blood-red Crossroads," said even violence had a rightful place in art.
"This is a wake-up call, a reminder that we shouldn't forget, and that we should face up to history and shouldn't hide from it," said Sheng, who is currently living in the U.K.
The authorities are also targeting Beijing's universities, the seat of the 1989 student movement, as the anniversary draws near.
A directive issued by the China University of Politics and Law's international education department and circulating on the Chinese Internet this week called on international students to take an out-of-town trip to "enjoy the natural scenery" on June 3-4.
The all-expenses-paid trip would include a number of activities, with a choice of the countryside near Beijing, or Inner Mongolia, the directive said.
A student at the university contacted by RFA confirmed that the directive was genuine, but said students were still unsure whether the trip would go ahead.
"The details aren't very clear, so I'm not really sure. I think it might have been canceled," the student said.
Beijing-based rights activist Hu Jia said the authorities had also stepped up controls on Chinese students at the capital's major universities, many of which are clustered together in the west of the city.
"For the past 25 years, there has been a tight surveillance program targeting Qinghua, Beijing University, Beijing Normal University and other schools like that on June 4," said Hu, who launched a bid to commemorate the crackdown this year with his "Return to Tiananmen" online campaign.
"There are large numbers of police cars and patrols on the campuses, particularly Beijing University," he said. "This has now been extended to some of the offices of overseas news organizations now, as well."
"State security police are now going directly to their offices and telling them that they mustn't carry out any interviews relating to June 4, nor must they go anywhere near Tiananmen Square," Hu said.
He said many Internet users had reported problems using Google services, including Gmail, ahead of the anniversary.
"You can't open it at all unless you use circumvention software," he said. "And if you use Google to search for 'June 4' or 'Tiananmen massacre', the screen just goes blank and white immediately."
"Also, you can't view any video or photos originating from IP addresses in Hong Kong and Taiwan."
Asked about the June 4, 1989 crackdown at a regularly scheduled news conference, Chinese Foreign Ministry spokesman Hong Lei did not refer directly to Tiananmen Square or the military action.
"Regarding the political incident which happened in the late 1980s in China, as well as issues related to it, the Chinese government reached a conclusion a long time ago," Hong said before launching into a defense of Beijing’s economic reforms.
Hong also denied cases of political persecution, saying: "In China, there are only law offenders. The so-called dissidents as you mentioned do not exist," the Associated Press reported.
The tight security on the ground isn't limited to Beijing, activists said on Tuesday.
"Sichuan is under tight security right now, with people being taken 'on vacation' or put in detention," Tianwang rights website founder Huang Qi said.
"I would say there are at least 300 people affected, and at least 100 from Chengdu," he said, referring to Sichuan's provincial capital.
"It's because we're approaching June 4, so there's a huge stability maintenance operation going on," Huang Qi said.
"Some petitioners have been getting text messages from the local government warning them they'll have a fight on their hands if they think of telling tales on them in Beijing."
China's leadership has ignored growing calls for a public reappraisal of the 1989 student protests, which the party once styled a "counterrevolutionary rebellion."
The number of people killed when PLA tanks and troops entered Beijing on the night of June 3-4, 1989 remains a mystery.
Beijing authorities once put the death toll at "nearly 300," but has never issued an official toll or list of names, and has always maintained that the violence was necessary to end the unrest.
Reported by Xin Yu and Yang Fan for RFA's Mandarin Service, and by Grace Kei Lai-see for the Cantonese Service. Translated and written in English by Luisetta Mudie.