Rounded up to be killed: ISIS militants seize dozens of Iraqi soldiers before driving them to the desert to be shot

Iraq's top military spokesman, Lt. Gen. Qassim al-Moussawi, confirmed the photos' authenticity today. He said he was aware of cases of mass murder of captured Iraqi soldiers in areas held by ISIS.

The full set of photos shows militants loading the men into flatbed trucks before forcing them to lie face-down in a shallow ditch with their arms tied behind their backs. The final images appear to show the bodies of the captives after being shot.

The grisly images could further sharpen sectarian tensions as hundreds of Shiites heed a call from a spiritual leader to take up arms against the Sunni militants that have swept across the north.

ISIS has vowed to take the battle to Baghdad and cities further south housing many Shiite shrines. Hundreds of Shiite men were today attending recruitment centres in Baghdad to be armed in response to a call by Grand Ayatollah Ali al-Sistani for Iraqis to defend their country

A car bomb meanwhile exploded in central Baghdad, killing 10 and wounding 21, according to police and hospital officials. Baghdad has seen an escalation in suicide and car bombings in recent months, mostly targeting Shiite neighbourhoods or security forces.

UN human rights chief Navi Pillay warned on Friday of 'murder of all kinds' and other war crimes in Iraq, and said the number killed in recent days may run into the hundreds, while the wounded could approach 1,000.

Speaking in Geneva, she said her office has received reports that militants rounded up and killed Iraqi soldiers as well as 17 civilians in a single street in Mosul.

Her office heard of 'summary executions and extrajudicial killings' after militants overran Iraqi cities and towns, the statement said.

However, despite the bloodshed, some Iraqis are already returning to Mosul after Islamist insurgents promised them cheap fuel and food, restored power and water, and the removal of barricades.

Many appeared excited to return, swelled with sectarian pride with the quick advances of the Islamic State of Iraq and the Levant, who Sunni Muslims regard as liberators.

But elsewhere, tens of thousands of others, mainly Shiites, are piling into refugee camps as they flee the deadliest conflict to grip Iraq since the 2003 U.S.-UK invasion.