China has intensified a campaign to silence dissidents and students in an attempt to make sure next week's 20th anniversary of the Tiananmen Square massacre goes unmarked.

Beijing has taken steps to prevent dissent in response to a groundswell of pressure for the authorities to atone for what happened.

Students at Beijing and Dalian Universities have been banned from giving any interviews to the foreign media until after the anniversary.

University exams have been scheduled across China on June 4, in what appears to be an attempt to keep students inside their classrooms.

Security officers have also been targeting known dissidents including Bao Tong, 76, an aide to Zhao Zhiyang, the late Chinese leader. He has been taken out of Beijing to the mountain region of Huangshan on Monday.