BEIJING - China's press and Internet sites were silent Friday over the 20th anniversary of the army crackdown on pro-democracy protests in and around Tiananmen Square.

There was a huge security clampdown on the square Thursday, 20 years after the events of June 4, 1989 in an attempt by authorities to prevent any commemoration of the bloody clampdown that left hundreds and perhaps thousands dead.

On Friday, China's strictly censored newspapers made no mention of the anniversary and the Internet was devoid of any article on 6/4, as it is referred to in Chinese.

China earlier this week blocked several popular websites, including search engine Bing, social networking service Twitter and photo-hosting website Flickr. These were still out of bounds Friday.

Only the official English-language China Daily referred fleetingly to the crackdown Friday in a story on China's opposition to US Secretary of State Hillary Clinton's remarks on the "20th anniversary of the events of June 4."

Clinton had made a public demand for an account of the dead and missing, but the newspaper made no further comment about the crackdown.

Even on the foreign ministry's website a transcript of a regular press conference held on June 4 and attended by AFP left out all questions asked by reporters about the Tiananmen crackdown.

That day, however, the English-language version of the state-controlled Global Times newspaper had carried an unusually bold article on the incident, calling it a "sensitive topic."

But David Bandurski, a researcher at the China Media Project at the University of Hong Kong, told AFP this did not signal any future relaxation in media control of the taboo subject.

"You can never, ever read the English-language Chinese media for signs of change on key issues, particularly press policy," he told AFP by email.

"This is an apartheid system of press controls, with one set of standards for Chinese media, and a whole different set for English-language media." -AFP