Reports that a Lebanese-Australian terrorist, notorious for holding up the severed heads of Syrian victims, has been killed fighting in Iraq have raised the potential for his young family to be repatriated from the Middle East, Australia's foreign minister said on Tuesday.

Australian intelligence agencies were attempting to verify the recent deaths of Australians Khaled Sharrouf and Mohamed Elomar in the Islamic State-held city of Mosul in Iraq, Foreign Minister Julie Bishop said. Both men were seen in photographs posted on social media holding heads of Syrians.

A U.S. airstrike in northern Iraq has killed an Islamic State operative who was a person of interest in the 2012 Benghazi attack, the Pentagon said Monday.

Pentagon spokesman Colonel Steve Warren said Ali Awni al-Harzi of Tunisia was killed in Mosul on June 15. 

Iraq's former premier and current vice president, Nuri al-Maliki, blamed "conspiracies" Saturday for the loss of major cities to jihadists and said Baghdad should prioritize paramilitaries over the army to fight them.

But Maliki, who was prime minister when the Islamic State jihadist group began a brutally effective offensive last year, failed to mention the role he and his government played in the debacle.

The Islamic State group Thursday released a propaganda documentary marking a year since it captured Mosul and recounting its surprise at how easily it took over Iraq's second city.

The film glamorizes the founding moment of the "caliphate" IS proclaimed less than three weeks later as an epic conquest but it also further documents the collapse of Iraq's security forces.

When the Iraqi government lost Ramadi last month, Abu Yasser's heart sank: the prospect of his own city, Mosul, shaking off jihadist rule had just faded farther into the distance.

Wresting back Mosul, Iraq's second city, was always seen as the top prize and climax of any fightback against the Islamic State group.

Iraqi security forces lost 2,300 Humvee armored vehicles when the Islamic State jihadist group overran the northern city of Mosul, Prime Minister Haider al-Abadi said on Sunday.

"In the collapse of Mosul, we lost a lot of weapons," Abadi said in an interview with Iraqiya state TV. "We lost 2,300 Humvees in Mosul alone."

Syrian and Iraqi Christians have pleaded for more international assistance from new homes in Lebanon where they recently arrived after fleeing attack by militants from the Islamic State group.

They spoke on Tuesday in two Beirut churches where they lined up to receive food baskets and other humanitarian assistance from a non-profit organization called In Defense of Christians (IDC), whose mission is to protect Christians in the Middle East.

Iraqi officials have expressed irritation and analysts skepticism at the U.S. prediction that an offensive to retake Iraq's key city of Mosul from jihadists could be launched in April-May.

Mosul is a major hub for the Islamic State group and holds special significance as the place where jihadist leader Abu Bakr al-Baghdadi proclaimed his "caliphate" straddling Iraq and Syria.

The U.S. wants Iraq to launch its offensive to retake the strategic northern city of Mosul from the Islamic State group in April or May, military officials said Thursday.

Mosul is believed to be held by 1,000-2,000 IS fighters and 20,000-25,000 Iraqi troops are needed to carry out the offensive, an official with U.S. Central Command said.

Kurdish forces backed up by U.S.-led air strikes have recaptured territory from Islamic State jihadists near the strategic city of Mosul in northern Iraq, the American military said Monday.

The advance is the latest push by Kurdish forces around Mosul, considered a crucial battleground for an eventual major counteroffensive against the IS group by Iraqi government troops and the Kurds.