Zhang Shijun, a former soldier, has publicly expressed regret over his role in the bloody 1989 crackdown on pro-democracy protests in Beijing's Tiananmen Square. (Elizabeth Dalziel/Associated Press)

A soldier who publicly expressed regret for his part in the bloody 1989 crackdown on pro-democracy rallies in Beijing's Tiananmen Square has been detained by Chinese police, according to a human rights group.

In an open letter posted on the internet, Zhang Shijun, 40, called on Communist party Leader Hu Jintao to reconsider the condemnation of the student-led rallies the happened almost 20 years ago.

A family member said he was taken from his home early Friday, according to the Civil Rights and Livelihood Watch, a mainland-based group.

Zhang was reached on his mobile phone Friday afternoon, but said, "it was not convenient to talk," before hanging up.

His wife said Friday she had not seen or heard from him.

Zhang is among only a few soldiers to speak publicly about the incident that sparked international outrage.

It is believed troops stormed into the square killing hundreds, possibly thousands of protesters on orders from top party leaders.

Zhang spoke about his experiences during the crackdown and about serving jail time later for alleged political crimes in an interview with the Associated Press on Tuesday.

The next day, he was ordered into his local police station and told to shun contact with foreign media, he said.

With files from The Associated Press