BAGHDAD, Iraq - A prominent female Iraqi human rights lawyer and campaigner has been publicly executed days after posting anti-ISIS messages on her Facebook page, the U.N. said Thursday. Samira Salih al-Nuaimi was killed by a masked firing squad in a public square in the city of Mosul, an act described as "horrifying" by the U.N. High Commissioner for Human Rights. She was tortured before her death on Monday, the U.N. said.

Al-Nuaimi, a well-known figure in Mosul, was remembered for her courageous work promoting the rights of women and helping the poor. "She used to stand before courts in order to defend those who were detained by U.S. forces, and she did that for free," a Mosul resident told NBC News. Al-Nuaimy was detained Sept. 17 after she posted messages on Facebook describing ISIS' bombing and destruction of mosques and shrines in Mosul as "barbaric." She was accused by the self-styled Islamic court of apostasy and sentenced to death by ISIS fighters. Her body will be handed to family who have been warned against conducting a funeral ceremony, a local journalist told NBC.

IN-DEPTH

- NBC's Baghdad Producer and Christina Boyle.