An Iranian woman protesting over death by stoning in Brussels
ISIS militants have publicly executed a female activist for criticizing the group in a Facebook post. (representational image).Reuters file

Human rights lawyer and activist Sameera Salih Ali al-Nuaimy has been publicly executed by the Islamic State for her alleged posts on Facebook that were critical of the group's destruction of shrines, churches, mosques and cultural sites in Mosul.

Reports indicate that the public execution of al-Nuaimy took place on 22 September after a quick trial by a Sharia court that found her guilty of apostasy.

The activist was executed by an ISIS firing squad in a busy market square in Mosul.

Prior to her execution, al-Nuaimy  is said to have been brutally tortured for five days in an attempt to force her to 'repent', the United Nations Assistance Mission for Iraq reported Thursday.

The ISIS, which also is known as ISIL, an acronym for Islamic State of Iraq and the Levant, took away al-Nuaimy from her house on 17 September over allegations that her posts criticized the Islamic State. She is also said to have labelled the militant group as 'barbaric.'

"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", Head of UN Assistance Mission in Iraq, Nickolay E. Mladenov said.

"ISIL has repeatedly targeted the weak and defenseless in acts of brutality and cowardice that are beyond description, bringing about unfathomable suffering to all Iraqis regardless of their gender, age, religion, faith or ethnicity", noted Mladenov, who is also the Special Representative of the Secretary General for Iraq.

Since it captured the city of Mosul, the Islamic State militants have thrown out thousands of Christians from the city and introduced Sharia law.

The Sunni militant group, which follows the most stringent and often the most brutal form of Islamic teachings, destroyed the tomb of Jonah in July, a prophet believed by Abrahamic faiths to have been swallowed by a whale or fish.

Sources from Mosul confirmed to CNN that ISIS operatives planted explosives around the mosque and detonated it remotely. The group even posted a video of the destruction.

Members of the militant group Islamic State in Iraq and Syria (ISIS) also have torched a 1,800 year-old Catholic Church in Mosul.