Chinese security forces have detained a former soldier who publicly expressed regret over his role in the 1989 military crackdown on pro-democracy protests near Tiananmen Square, a human rights group said Friday.

The former soldier, Zhang Shijun, 40, published an open letter to Hu Jintao, the Communist Party leader, on the Internet in which he called on the party and government to reconsider its condemnation of the student-led protests.

He said he hoped his example would inspire more former soldiers to come forward and form a network, but he appeared reluctant to cast himself as an organizer, perhaps wary of the party's tendency to single out perceived opposition ringleaders for harsher punishment.