China has released three prominent members of the Tiananmen Mothers' Organisation, whose relatives were killed in the 1989 crackdown.
The women's relatives were killed in the suppression of the protests
They were detained earlier this week, apparently for trying to import T-shirts printed in English commemorating the pro-democracy protests.
The official Xinhua news agency said the three "conspired with overseas forces to evade Chinese customs".
Authorities appear to be uneasy as the 15th anniversary of the protests nears.
The released women were Ding Zilin, a retired professor whose 17-year-old son was killed during the 1989 crackdown by Chinese security forces. She has been a prominent member of the organisation and is reported to have been helping other bereaved relatives.
The other two were Zhang Xianling, whose 19-year-old son was killed, and Huang Jinping, who lost her 30-year-old husband.
On Friday, Ms Ding's husband, Jiang Peikun, told Reuters news agency he was angry about the official reason given for his wife's detention.
"Can you see how this violates national security? Do you believe the report? I don't believe it," he said.
According to earlier reports, the three were detained because the mothers' group planned to submit evidence about Tiananmen to a UN human rights conference meeting in Geneva.
The Tiananmen protests were triggered by the death on 15 April 1989 of pro-reform leader Hu Yaobang.
China regularly steps up security ahead of the anniversary, especially in the capital Beijing.
Several hundred people were killed by security forces around Tiananmen Square on 4 June.
According to most analysts, the episode remains too sensitive for the ruling Communist Party to re-assess.