BEIJING (AP) ― Beijing put additional police on the street and detained government critics Tuesday as part of a security crackdown on the eve of the 25th anniversary of the crushing of pro-democracy protests centered on the capital’s Tiananmen Square.

Police manned checkpoints on Tuesday and officers and paramilitary troops patrolled over pedestrian overpasses and streets surrounding the square in the city center.

The increased security comes on top of heightened restrictions on political activists, artists, lawyers and other government critics. Dozens have been taken into detention, forced out of Beijing or confined to their homes in other parts of the country.

“June 4 has come again and the plainclothes officers are here to protect us. I can’t leave the house to travel or lecture,” said Jiangsu province-based environmental activist Wu Lihong in a text message.

Artists and former activist Guo Jian was also taken away by authorities on Sunday night, shortly after a profile of him appeared in the Financial Times newspaper in commemoration of the crackdown’s anniversary. As he was being detained, Guo, an Australian citizen, told an Associated Press reporter he would be held until June 15.

A writer and officer of the Independent Chinese PEN Center, who goes by the pen name Ye Du, was also taken from his home in the southern city of Guangzhou to join in a forced “tour trip,” his wife, Wang Haitao, said by phone. Such compulsory trips are a common method of keeping government critics under 24-hour watch without the need to initiate a legal process.

China allows no discussion of the events of June 3-4, 1989, when soldiers accompanied by tanks and armored personnel carriers fought their way into the heart of the city, killing hundreds of protesting citizens and onlookers. The government has never issued a complete, formal accounting of the crackdown and the number of casualties involved.

Beijing’s official verdict is that the student-led protests aimed to topple the ruling Communist Party and plunge China into chaos. Protest leaders said they were merely seeking greater democracy and freedom, along with an end to corruption and favoritism within the party.

Authorities regularly tighten security ahead of June 4, but this year’s suppression has notably harsher than in past. Activists who in past would receive no more than a warning have been taken into custody and police have told foreign journalists they would face unspecified serious consequences for covering sensitive issues ahead of the anniversary.

A French broadcaster said its journalists were interrogated for six hours by Beijing police when they were found interviewing people on the street about the events 25 years ago.

Despite China’s discouragement, the crackdown is recalled with rallies and commemorations in Chinese communities worldwide, especially in Hong Kong, a former British colony that retains its own legal system and civil liberties since returning to Chinese rule in 1997.

Thousands marched through the city on Sunday in remembrance of the crackdown, and organizers said they expected about 150,000 people to join in a candlelight vigil in a city park Wednesday.