BEIJING  Last Saturday was tomb-sweeping day, when the Chinese traditionally honor the dead. Sun Wenguang, a 75-year-old retired professor, was one of many to visit the cemetery.

Apparently, though, he chose the wrong death to commemorate. He came to remember Zhao Ziyang, a former prime minister and Communist Party general secretary who lost his party position and his freedom after sympathizing with student-led, pro-democracy protests in Tiananmen Square in 1989. Mr. Zhao, who died in 2005, is a martyr to some democracy advocates.

As Mr. Sun entered the cemetery in Jinan, a city about 230 miles south of Beijing, he said, four or five men attacked him and beat him severely. He is now in a Jinan hospital with three broken ribs and injuries to his spine, head, back, arms and legs, according to China Human Rights Defenders, a Hong Kong-based group. The group said the attack on Mr. Sun was part of a concerted effort by the Chinese government to head off any efforts to memorialize the deaths of hundreds of Tiananmen Square protesters on June 4, the 20th anniversary of the government’s crackdown.

“Chinese authorities are staging a campaign of terror to intimidate and suppress expressions of commemoration for the 1989 Tiananmen massacre,” the group said in a statement. The attack on Mr. Sun “is part of the overall campaign,” it said.