A 12-year-old Christian girl burned to death in her own home by ISIS terrorists in Mosul, northern Iraq, used her last words to urge her family to forgive her murderers.

The girl's mother revealed her daughter's dying wish as she spoke of ISIS's brutal reign of terror in the Iraqi city and the oppression suffered by Christians in the area.

Jihadi fighters had come to claim a religious tax from the girl's mother, paid by all non-Muslims in ISIS-controlled areas, but when the mother delayed in paying, they burned down the family home.

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'Punished': The 12-year-old girl was burned to death in her own home by ISIS terrorists in Mosul, northern Iraq when her mother delayed in paying a religious tax imposed on Christians and other non-Muslims

The mother described how 'foreign ISIS fighters' had come to their home in Mosul to claim Jaziya, a religious tax imposed on non-Muslims.

'The ISIS foreign fighters were at her door and they told her "you have two choices, you are to leave now or you are to pay the Jaziya",' Jacqueline Isaac, a human rights advocate, told the Express,.

'She said "I will pay, give me a few seconds my daughter is in the shower". They said 'you don't have a few seconds" and they lit the house with a torch.'

Mother and child were able to escape the burning building, but the girl had suffered such severe burns that she later died in hospital.

Ms Isaac added: 'Her daughter died in her arms. The last thing her daughter said: "Forgive them".'

ISIS supporters chant slogans as they wave the group's flags in front of the provincial government headquarters in Mosul, northwest of Baghdad, Iraq after taking power in June 2014

The brutal murder of the young Christian girl is one of several horrific ISIS executions carried out in Mosul this week, as the terrorist group continues to lose territory in Iraq.

Earlier on Thursday, local news reported that ISIS has executed 25 people in Mosul by lowering them in a vat of nitric acid until their organs dissolved.

The more than two dozen men had been accused of spying on ISIS on behalf of Iraqi government security forces.

The executions in Mosul follows a number of deadly bombings in the capital Baghdad, as ISIS hopes to rebound from their battlefield losses in Iraq.

The terrorist group has continued losing control over territory across Iraq and Syria, a U.S. Military spokesman said this week, including almost half of what it had once held in Iraq.

Losing ground: Fighters from the Iraqi pro-government forces flash the sign for victory as they drive vehicles in the Albu Aitha area, north of Ramadi, Iraq, where ISIS has lost more than half of its territory

The U.S. Defense Department had previously estimated that ISIS fighters had lost control of about 40 per cent of the territory they claimed in Iraq and about ten per cent of the land they held in Syria.

Those tallies had gone up in recent weeks, Pentagon spokesman Peter Cook said.

'The number right now in Iraq is about 45 per cent of the territory they once held has been recovered,' Cook said.

'The number in Syria is anywhere between 16 to 20 per cent.'

ISIS stormed across large parts of Iraq and Syria in early 2014, meeting little resistance from Iraqi security forces and exploiting the chaos in civil-war-torn Syria.

Since August 2014, the United States has led an international coalition fighting back against the IS group, using a combination of air strikes and training and equipping local partners.

ISIS has now lost control of Ramadi and Heet in Iraq, but still control other important cities including Mosul and Fallujah.