New Delhi, June 5 -- Chinese authorities snuffed out efforts to mark Thursday's anniversary of the deadly 1989 military crackdown on student-led pro-democracy protests in Tiananmen Square, in a further tightening of a yearslong campaign to erase what happened from public memory.

Police told relatives of the victims they would not be allowed to visit a cemetery in Beijing on the anniversary of the crackdown 37 years ago, a person with knowledge of the matter said. The person spoke on condition of anonymity because of fear of retribution.

Relatives from a group called Tiananmen Mothers visited the graves for more than 30 years, reading memorial statements while police kept watch, Amnesty International said.

Hundreds of people, and possib...