The United Nations says militants with the Islamic State group have publicly killed a rights lawyer in the Iraqi city of Mosul after finding her guilty of apostasy in a self-styled Islamic court.

The UN Assistance Mission in Iraq says Samira Salih al-Nuaimi was seized from her home on Sept. 17 after allegedly posting messages on Facebook that were critical of the militants' destruction of places of worship in Mosul.

The Gulf Center for Human Rights said Wednesday that al-Nuaimi had worked on detainee rights and poverty.

The extremist Islamic State group seized Iraq's second largest city Mosul in June during its rapid advance across the country's north and west. It has imposed a harsh version of Islamic law in areas under its control in Iraq and Syria.