The battle to retake the Iraqi city of Mosul from jihadists could unleash a massive humanitarian crisis, potentially pushing hundreds of thousands to flee their homes as winter sets in.

Mosul, the country's second city, was seized by the Islamic State group in 2014, and is now the last major population centre in Iraq still held by the jihadists, who have lost much of the territory they seized two years ago.

The Islamic State group has abducted 48 media workers in its Iraqi stronghold of Mosul since June 2014 and executed at least 13 of them, watchdogs said.

Since the jihadists took over Iraq's second city in June 2014, at least 60 journalists, citizen journalists and media workers have fled, according to a report published late Tuesday by Reporters Without Borders (RSF).

Top officials ignored ample warnings of an impending attack on Iraq's second city Mosul and grossly mismanaged the crisis that saw jihadists seize it, a parliamentary report obtained by AFP says.

The Islamic State (IS) jihadist group's capture of Mosul in June 2014 might have been avoided if senior officers and officials had performed competently and acted on multiple detailed intelligence reports warning of the attack.

Former Iraqi premier Nuri al-Maliki Tuesday dismissed as "worthless" a parliamentary report blaming him and others for the jihadist takeover of second city Mosul last year. 

"There is no value in the result that emerged from the parliamentary investigation committee on the fall of Mosul, which was dominated by political differences and was not objective," Maliki said on his Facebook page.

Iraqi lawmakers voted Monday to refer to the judiciary a report holding top officials, including ex-premier Nuri al-Maliki, responsible for the fall of second city Mosul, the parliament speaker said.

But there were disagreements over the report, with MPs voting to send it without an official reading, and members of the investigative committee that compiled it complaining that there was no vote to approve the recommendations it contained.

The Islamic State group has executed more than 2,000 people in and around the northern Iraqi city of Mosul since seizing it last year, officials said Friday.

Parliament speaker Salim al-Juburi confirmed "the execution of more than 2,000 innocent citizens at the hands of the terrorist Daesh organization," his office said, using an Arabic acronym for IS.

Christian clerics prayed in the ruins of a monastery not far from jihadist positions in northern Iraq Thursday to mark a year since the exodus of Iraq's Christians from nearby ancestral lands.

"We want the good people to hear our prayers from this place so they hurry and liberate our areas as quickly as possible," Yohanna Boutros Moshe, the Syrian Catholic Archbishop of Mosul, told AFP.

The Islamic State group has executed an Iraqi journalist in the northern city of Mosul on charges of spying, local officials and colleagues said Saturday.

Jala al-Abadi was taken from his home with his phone and laptop on June 4 and executed on Wednesday by firing squad after being sentenced by an IS court.

With wooden crosses around their necks and others tattooed on their arms, several dozen Iraqi Christians are training to recapture their homes overrun by the Islamic State jihadist group.

A year ago, IS launched a fierce offensive in northern Iraq, quickly capturing second city Mosul, with its large Christian minority, and Christian-populated areas in the surrounding Nineveh province.

The mother-in-law of one of a Lebanese man and Australia's most notorious Islamic State fighters has pleaded for the government to help her "desperate" daughter and five grandchildren flee the Middle East, saying she made "the mistake of a lifetime.”

Karen Nettleton's emotional appeal for help came after reports that her son-in-law Khaled Sharrouf and his friend Mohamed Elomar were killed in fighting in the Iraqi city of Mosul in the past week, although officials Wednesday suggested they may have died in Syria .