( CNN ) -- A demonstration erupted Sunday outside an Iranian detention center , where 33 members of a women 's group were being held following their arrest during a peaceful protest in a Tehran park a day before , a human rights organization reported . The International Campaign for Human Rights in Iran , citing an eyewitness account , said more than 100 police and plainclothes officers broke up a gathering of the Mourning Mothers in Laleh Park on Saturday afternoon . The group , formed by women whose children have been killed in recent anti-government protests , gathers every weekend at the park to call attention to the deaths . `` They would not allow anyone to even sit on the benches or congregate , '' the organization quoted the unidentified witness as saying . `` After about 70 mothers entered the park , security forces engaged them and started chasing them , grabbing them , and forcing them into police vans . They used a lot of violence and insults in the process . '' Thirty-three women were taken to the Vozara Detention Center , said Hadi Ghaemi , director of the human rights campaign . Later , nine women were taken to emergency rooms in two hospitals , but all nine were returned to the detention center late Saturday , he said Sunday . Families and other group members went to the detention center Sunday to demand answers to why the women were detained . Officials provided the names of those detained . Those gathered outside the detention center Sunday were alarmed about the health of those inside when an ambulance entered the center , Ghaemi said . The gathering turned into a protest , with people chanting , `` Free the mothers ! '' Security forces attacked the crowd to disperse it , Ghaemi said . Two people passing by in a car who took pictures were placed in the detention center , he said . With Iran 's tight restrictions on international media , CNN could not independently verify the report . The group 's Web site had no details about the reported arrests . `` No culture permits such violence to be unleashed against mothers , '' Ghaemi said in a news release posted on the campaign 's Web site . `` How can this government , which claims to have moral and religious authority , treat mothers who have lost their children in such a way ? The Iranian officials should know that the activities of Mourning Mothers will not stop until their legitimate grievances are properly addressed . '' Mourning Mothers was formed after the violent crackdown on anti-government demonstrators following the disputed June 12 presidential vote , which re-elected hardline President Mahmoud Ahmadinejad over main opposition candidate Mir Hossein Moussavi . Since then , opposition activists and mothers whose children have disappeared or have been executed or detained have also joined the group . Among its members is the mother of 26-year-old Neda Agha-Soltan , whose chilling death in post-election protests was caught on video and became a powerful symbol for the opposition . The mothers are demanding government accountability for the deaths , disappearances and detentions of their children .
NEW : Security forces Saturday dispersed crowd protesting women 's arrests , group says . Rights group : more than 100 women 's group members arrested Sunday by Iranian security forces . Arrests made during a peaceful protest in a Iran park on Saturday , rights group says . Group formed by women whose children were killed in recent anti-government protests .