DUBAI, United Arab Emirates (AP) — Rights groups say people associated with a U.S.-based Iranian activist who advocates against the Islamic Republic's mandatory hijab for women have been detained.

Amnesty International and the Center for Human Rights in Iran said Wednesday that the arrests targeted people linked to Masih Alinejad.

Alinejad founded the "White Wednesdays" campaign to encourage Iranian women to post photographs of themselves without headscarves online as a way of opposing the compulsory hijab.

Amnesty said those detained on Tuesday included her brother and the brother and sister of her ex-husband. It said one of them has already been released.

Iranian officials and its state media did not immediately acknowledge the arrests.

In July, officials said any Iranian sending images to the campaign could face up to 10 years in prison.