Chinese honor guard soldiers stand in position Wednesday against the backdrop of Tiananmen Square in Beijing. Foreign journalists were barred from Beijing’s Tiananmen Square on the eve of the 20th anniversary of pro-democracy protests crushed by the government.

Beijing ? A massive police presence ringed China’s iconic Tiananmen Square today, the 20th anniversary of the bloody crackdown on pro-democracy activists, as the government continued an overwhelming drive to muzzle dissent and block commemorations.

An exiled protest leader — famous for publicly haranguing one of China’s top leaders 20 years ago — was also blocked from returning home to confront officials over what he called the “June 4 massacre.”

Foreign journalists were barred from the vast square as uniformed and plainclothes police stood guard across the vast plaza that was the epicenter of the student-led movement that was crushed by the military on the night of June 3-4, 1989.

Security officials checking passports also blocked foreign TV camera operators and photographers from entering and covering the raising of China’s national flag, which happens at dawn every day. Plain clothes officers aggressively confronted journalists on the streets surrounding the square, cursing and threatening violence against them.

The heavy security moves come after government censors shut down social networking and image-sharing Web sites such as Twitter and Flickr, and blacked out CNN when it airs stories on Tiananmen.

Dissidents were confined to their homes or forced to leave Beijing, part of sweeping efforts to prevent online debate or organized commemorations of the anniversary.

In another 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, 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. He told The Associated Press by phone he spent the night at the Macau airport’s detention center, and immigration officials planned to deport him to Taiwan on Thursday.

The denial of entry on the Tiananmen anniversary was a “tragedy,” Wu’er said.

Wu’er rose to fame in 1989 as a pajama-clad hunger striker yelling at 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 now lives in exile in the self-ruled island of Taiwan. 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 leave China.

The student leader who topped the most-wanted list, Wang Dan, was jailed for seven years before being expelled to the United States in 1998.

In Washington, U.S. Secretary of State Hillary Rodham Clinton said in a statement Wednesday that China, as an emerging global power, “should examine openly the darker events of its past and provide a public accounting of those killed, detained or missing, both to learn and to heal.”