BAGHDAD (AP) — Militants with the Islamic State group publicly killed a rights lawyer in the Iraqi city of Mosul after finding her guilty of apostasy in a self-styled Islamic court, the U.N. mission in Iraq said Thursday.

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 religious sites in Mosul.

According to the United Nations Assistance Mission in Iraq, al-Nuaimi was tried in a so-called “Sharia court” for apostasy, after which she was tortured for five days before the militants sentenced her to “public execution.”

She was killed on Monday, the U.N. mission said. Her Facebook page appears to have been removed since her death.

“By torturing and executing a female human rights’ lawyer and activist, defending in particular the civil and human rights of her fellow citizens in Mosul, ISIL continues to attest to its infamous nature, combining hatred, nihilism and savagery, as well as its total disregard of human decency,” Nickolay Mladenov, the U.N. envoy to Iraq, said in a statement, referring to the group by an acronym.

The militant group captured Iraq’s second largest city Mosul during its rapid advance across the country’s north and west in June, as Iraqi security forces melted away. The extremists now rule a vast, self-declared caliphate straddling the Syria-Iraq border in which they have imposed a harsh version of Islamic law and beheaded and massacred their opponents.

In the once-diverse city of Mosul, the group has forced religious minorities to convert to Islam, pay special taxes or die, causing tens of thousands to flee. The militants have enforced a strict dress code on women, going so far as to veil the faces of female mannequins in store fronts.

In August, the group destroyed a number of historic landmarks in the town, including several mosques and shrines, claiming they promote apostasy.

The Gulf Center for Human Rights said Wednesday that al-Nuaimi had worked on detainee rights and poverty. The Bahrain-based rights organization said her death “is solely motivated by her peaceful and legitimate human rights work, in particular defending the civil and human rights of her fellow citizens in Mosul.”

In the nearby town of Sderat, militants on Tuesday broke into the house of a female candidate in the last provincial council elections, killed her and abducted her husband, the UN also said. On the same day, another female politician was abducted from her home in eastern Mosul and remains missing.

The Islamic State extremists’ blitz eventually prompted the United State to launch airstrikes last month, to aid Kurdish forces and protect religious minorities in Iraq.

This week, the U.S. and five allied Arab states expanded the aerial campaign into Syria, where the militant group is battling President Bashar Assad’s forces as well as Western-backed rebels.

Nearly a dozen countries have also provided weapons and training to Kurdish peshmerga fighters, who were strained after months of battling the jihadi group.

In other developments Thursday, German Defense Minister Ursula von der Leyen visited northern Iraq for talks with Kurdish leaders about the fight against Islamic State extremists and Berlin’s efforts to help with arms deliveries.

Thursday also marked the start of German arms deliveries to the semi-autonomous Kurdish region, with the ultimate goal of supplying 10,000 Kurdish fighters with some 70 million euros ($90 million) worth of equipment.

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Associated Press writer David Rising in Berlin contributed to this report.