BEIJING — Chinese human-rights activists yesterday released the names of 13 people still in prison 18 years to the day since the Tiananmen Square massacre.

The list is the most comprehensive recent effort to trace those who were arrested in the wake of the massacre but have not been seen since. Most of the high-profile student leaders involved in the pro-democracy demonstrations who did not go into exile have already been released.

Those still detained include several men convicted of crimes no worse than “counterrevolutionary sabotage,” a vague term often used to cover minor offenses involving protests against property.

In their statement, the group Chinese Human Rights Defenders said those named were Beijing residents, some of whom were accused of participating in violent activities but who may have been involved only in peaceful protest or self-defense.

As well as the 13 in prison, all serving the equivalent of life terms, the statement gave 10 names of those executed immediately afterward.

“Those who were sentenced to death, many of whom were executed immediately, or given long prison terms … tended to be ordinary people or workers, while the world focused its condemnation on cases of jailed students and intellectuals,” the statement said.

The massacre remains a taboo subject within mainland China. It is one of the so-called “Three Ts,” the others being Taiwan and Tibet, about which nothing can be said in the press without clear Communist Party direction.

In line with annual practice, some dissidents were put under house arrest in advance of the anniversary. But older dissidents have reported a loosening of conditions this year.