(Andy Wong ~ Associated Press)
Along with more common methods of muzzling dissent, the authorities extended their efforts Tuesday to silence social networking sites that might foster discussion of any commemoration of the events of June 3 and 4, 1989.
The action is a new sign of the government's concern of the potential of such technology in an authoritarian society where information is tightly controlled.
"There has been a really intensified clampdown on quasi-public discussion of awareness of this event," said Xiao Qiang, adjunct professor of the Graduate School of Journalism at the University of California-Berkeley, and director of The Berkeley China Internet Project.
"It's a discussion about where China is now and where China can go from here. So the authorities are making a major crackdown to block user-generated sites such as Twitter and show there is no right to public discussion," he said.
China has the world's largest online population, and Internet communities have proven increasingly influential in spreading word of events to everything from student protests to group shopping excursions.
People are going outside the normal, controlled channels to set up communities online, spreading information about campus unrest and other activities that the government considers to be potentially subversive.
Government Internet monitors have shut down message boards on more than 6,000 websites affiliated with colleges and universities, apparently to head off any talk about the 1989 events, according to the Hong Kong-based Information Center for Human Rights and Democracy.
Numerous blogs maintained by edgy government critics such as avant-garde artist Ai Weiwei have been blocked and the text-messaging service Twitter and photo sharing site Flickr could not be accessed within China on Tuesday. Video sharing site YouTube has been blocked within China since March.
"We understand the Chinese government is blocking access to Flickr and other international sites, though the government has not issued any explanation," said Jason Khoury, spokesman for Yahoo, which owns Flickr. "We believe a broad restriction without a legal basis is inconsistent with the right to freedom of expression."
Officials from Twitter did not responded to a request for comment.
Authorities have been steadily tightening surveillance over China's dissident community ahead of this year's anniversary, with some leading writers already under house arrest for months.
Government critics, including activist Ding Zilin and former top government adviser Bao Tong, could not be reached amid reports that they had been ordered to leave the capital before the anniversary of the crackdown.
Bao, the 76-year-old former secretary to Zhao Ziyang, the Communist Party leader deposed for sympathizing with the 1989 pro-democracy protesters, had gone to his native province of Zhejiang and would not return for another week, according to a woman answering the phone at his Beijing apartment and identifying herself as the housemaid. She refused to say when he left Beijing or provide contact numbers for him in Zhejiang.
Ding, a retired professor and advocate for Tiananmen victims whose teenage son was killed in the crackdown, had said earlier that security agents "strongly suggested" she and her husband leave the capital during the anniversary. Repeated calls to her Beijing home met with busy signals.
Elsewhere, in the Zhejiang province city of Taizhou, former educator Wu Gaoxing -- jailed for two years after the crackdown -- was taken from his home by agents Saturday, shortly after the publication of a letter he had co-signed complaining about economic discrimination against dissidents, according to another of the letter's signatories, Mao Guoliang.
China has never allowed an independent investigation into the military's crushing of the 1989 protests, in which possibly thousands of students, activists and ordinary citizens were killed. The subject remains taboo on the mainland, with officials routinely countering questions about Tiananmen with remarks on how much China has developed and prospered in the years since.
"The party and the government long ago reached a conclusion about the political incident that took place at the end of the 1980s and related issues," Foreign Ministry spokesman Qin Gang said at a regularly scheduled news conference Tuesday.
Despite the official silence, the crackdown remains a major topic for human rights groups and pro-democracy supporters in Chinese-ruled Hong Kong autonomous region, where this year's June 4 vigil is expected to draw tens of thousands.
Overseas monitoring groups estimate that 30 men remain imprisoned on charges relating to the protest, and Amnesty International issued an open letter this week to China's top legislator, Wu Bangguo, calling for their release.
Also Tuesday, exiled former student leader Chai Ling issued a rare public statement calling for the release of political prisoners, an independent investigation into the events, and permission for former student leaders to return home.
"The current generation of leaders who bear no responsibility should have the courage to overturn the verdicts" on the protests, said Chai's statement, distributed by the Hong Kong human rights center.