(AP) -- Police saturated Tiananmen Square with security Thursday, the 20th anniversary of the bloody crackdown on pro-democracy activists, and an exiled protest leader was blocked from returning home to confront Chinese officials over what he called the "June 4 massacre."
Foreign journalists were barred from the vast square as both uniformed and plainclothes police fanned out across the plaza that had been the epicenter of the student-led movement that was crushed by the military on the night of June 3-4, 1989.
The square was closed Wednesday for a welcoming ceremony for the prime minister of Malaysia and had not been reopened as of midnight. Tiananmen Square is usually closed only temporarily during important events such as the opening of the annual legislative session.
Authorities also shut down social networking and image-sharing Web sites such as Twitter and Flickr, and authorities confined dissidents to their homes or forced them to leave Beijing, part of sweeping efforts to prevent online debate or organized commemorations of the anniversary.
In a further sign of the government's unwavering hard-line stance toward the protests, the second most-wanted student leader from 1989 said he had been denied entry to the southern Chinese territory of Macau.
Wu'er Kaixi, who has been in exile since fleeing China after the crackdown, traveled to Macau on Wednesday to turn himself in to authorities in a bid to return home. Immigration officers pulled him aside and demanded he fly back to Taiwan, something he vowed to resist.
"I'm just waiting. I'm guessing they're waiting for instructions from their superiors," Wu'er told The Associated Press by phone, adding that he was being detained in a small room guarded by a lone official at the Macau airport's immigration offices.
"If they disagree with my behavior, they can arrest me. I can accept that," he said. "But I won't let them deport me."
Wu'er rose to fame in 1989 as a pajama-clad hunger striker haranguing then-premier Li Peng at a televised meeting during the protests. Named No. 2 on the government's list of 21 most-wanted student leaders after the crackdown, he escaped and has lived in exile in the self-ruled island of Taiwan, where he has worked as a businessman and political commentator. An attempt to return home in 2004 was rebuffed when he was deported from the Chinese territory of Hong Kong.
Wu'er said in a statement issued through a friend that he wants to turn himself in to the Chinese authorities so he can visit his parents - who haven't been allowed to visit him in Taiwan - and engage the government in a public dialogue about Tiananmen through his court trial.
"When I turn myself in, I will use the platform of a Chinese courtroom to debate the Chinese government about this incident," he said.
Wu'er added he believes he did nothing wrong in the 1989 protests.
"My turning myself in should not be interpreted as my admission that my behavior 20 years ago is illegal and wrong. I want to reassert here the Chinese government bears complete and undeniable moral, political and legal responsibility for the tragedy that happened in China in 1989," his statement said.
"I hope, 20 years later, the Chinese government can set a new position on the historical problem of the 'June 4 massacre,' admit its guilt and apologize to the Chinese people," he said.
The student leader who topped China's most-wanted list, Wang Dan, was jailed for seven years after the crackdown before being expelled to the United States in 1998. He was in Taiwan this week to attend commemorations there.
Beijing has never allowed an independent investigation into the military's crushing of the protests, in which possibly thousands of students, activists and ordinary citizens were killed. Young Chinese know little about the events, having grown up in a generation that has largely eschewed politics in favor of nationalism and economic development.
There were no signs of attempts to mark the protests in mainland China, where the government squelches all discussion of the events.
As in past years, foreign media reports on issues related to the protests in print, on television or the Internet were blocked. Journalists trying to film on the square or interview dissidents in recent days have been detained for several hours on apparently trumped-up charges of creating disturbances, according to the Foreign Correspondents Club of China.
Authorities have been tightening surveillance of China's dissident community ahead of the anniversary, with some leading writers already under close watch or house arrest for months.
Ding Zilin, a retired professor and advocate for Tiananmen victims, said by telephone that a dozen officers blocked her and her husband from leaving their Beijing apartment Wednesday.
"They won't even allow me to go out and buy vegetables," said Ding, whose teenage son was killed in the crackdown. "They've been so ruthless to us that I am utterly infuriated," she said.
Another leading dissident voice, Bao Tong, was taken by police to southeastern China, said his son, Bao Pu.
Bao Tong, 76, is the former secretary to Zhao Ziyang, the Communist Party leader deposed for sympathizing with the pro-democracy protesters.
All seven of the former student leaders on the original wanted list who remain in China were under surveillance and had been warned by police not to travel outside their home cities or accept media interviews, according to the Hong Kong-based Information Center for Human Rights and Democracy. Apart from Wu'er, those still on the list live in the United States and are barred from returning.
The blocking of social networking sites marked a new chapter in China's attempts to muzzle dissent and control information, showing the burgeoning influence of such technology among young Chinese.
Authorities targeted message boards on more than 6,000 Web sites affiliated with colleges and universities, along with Chinese mini-blogging site Fanfou and video sharing site VeryCD. Notices on their home pages said they would be closed through Saturday for "technical maintenance." The video site YouTube has been blocked in China since March.
Jason Khoury, spokesman for Yahoo, which owns Flickr, said no explanation had been given and the company believed the restrictions were "inconsistent with the right to freedom of expression." Officials from Twitter did not comment.
In Hong Kong, where the anniversary is openly commemorated, a second dissident who took part in the 1989 events was denied entry to the territory. U.S. Consulate General spokesman Dale Kreisher said the decision to deport Xiang Xiaoji, an American citizen, was "particularly regrettable in light of Hong Kong's well-known reputation as an open society."
Xiang had planned to attend Hong Kong's annual candlelight vigil for victims of the crackdown.
Associated Press writer Min Lee in Hong Kong contributed to this report.
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